Assessing sediment particle-size effects on benthic algal colonisation and total carbohydrate production

Journal Pre-proof Assessing sediment particle-size effects on benthic algal colonisation and total carbohydrate production

Tatenda Dalu, Ross N. Cuthbert, Tiyisani L. Chavalala, P. William Froneman, Ryan J. Wasserman PII:

S0048-9697(19)36344-2

DOI:

https://doi.org/10.1016/j.scitotenv.2019.136348

Reference:

STOTEN 136348

To appear in:

Science of the Total Environment

Received date:

5 November 2019

Revised date:

23 December 2019

Accepted date:

24 December 2019

Please cite this article as: T. Dalu, R.N. Cuthbert, T.L. Chavalala, et al., Assessing sediment particle-size effects on benthic algal colonisation and total carbohydrate production, Science of the Total Environment (2018), https://doi.org/10.1016/ j.scitotenv.2019.136348

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© 2018 Published by Elsevier.

Journal Pre-proof

Assessing sediment particle-size effects on benthic algal colonisation and total carbohydrate production

Tatenda Dalu a, b,*, Ross N. Cuthbert c, Tiyisani L. Chavalala d,e, P. William Froneman e, Ryan J Wasserman f

Aquatic Systems Research Group, Department of Ecology and Resource Management,

University of Venda, Thohoyandou 0950, South Africa

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a

Stellenbosch Institute for Advanced Study, Stellenbosch 7600, South Africa

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School of Biological Sciences, 19 Chlorine Gardens, Queen’s University Belfast, Belfast

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b

Freshwater Biodiversity Unit, South Africa National Biodiversity Institute, Kirstenbosch

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d

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BT9 5DL, Northern Ireland

Research Centre, Claremont 7735, South Africa

Africa f

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Department of Zoology and Entomology, Rhodes University, Grahamstown 6140, South

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e

Department of Biological Sciences and Biotechnology, Botswana International University of

Science and Technology, Palapye, Botswana *Corresponding author e–mail address: [email protected]

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Journal Pre-proof ABSTRACT Increased sedimentation and siltation associated with anthropogenic environmental change may alter microbial biofilms and the carbohydrates they produce, with potential bottom-up effects in these ecosystems. Therefore, the present study aimed to examine to what extent carbohydrate (associated with biofilm exopolymer) concentration and benthic algal biomass vary among different sediment types (size-structure categories) using a microcosm experiment conducted over a period of 28 days. Substrate treatment and time had a

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significant effect on the total chlorophyll-a concentrations, whilst a significant interaction

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was present in the case of total sediment carbohydrates. Total sediment carbohydrates did not

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relate significantly to chlorophyll-a concentrations overall, nor for any substrate treatments

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owing to a non-significant ‘chlorophyll-a × substrate’ interaction term. The diatom community characteristics across sediment sizes were unique for each treatment in our study,

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with unique dominant diatom taxa compositions within each sediment size class. The finest

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sediment particle-size (<63 µm) may be the least stable, most likely due to lower binding. We anticipate that the current study findings will lead to a better understanding of how different

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sediment types due to sedimentation and siltation will impact on primary productivity and the composition of diatom communities in aquatic systems.

Key words: sediment, carbohydrate, exopolymer production, benthic algae, chlorophyll-a

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Journal Pre-proof 1. Introduction Littoral zone soft-sediments of freshwater aquatic ecosystems (i.e. rivers, reservoirs, lakes and shallow waterbodies) are highly productive and critical habitats for invertebrates and vertebrates (Porej and Hetherington, 2005; Wang et al., 2006). Within this zone, microbial biofilms comprising diatoms, protozoa and fungi are especially important in processes affecting sediment stability through extracellular polymeric substance (EPS) secretion which contain high carbohydrate contents (Underwood et al., 1995; Underwood and Paterson, 2003;

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Takahashi et al., 2010; Xu et al., 2013; Gerbersdorf and Wieprecht, 2015; Cochero et al.,

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2017). Diatoms are major components of biofilms and significantly contribute to freshwater

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primary production and aquatic sediment stabilisation through inter-grain binding (Sutherland

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et al., 1995; Yallop et al., 2000), while heterotrophic prokaryotes (i.e. protozoa, bacteria and fungi) are primary organic matter re-mineralisers (Van Colen et al., 2013). These biofilms

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further regulate energy transfer through benthic food webs, acting as a major food source for

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primary consumers, either directly or indirectly (Carpentier et al., 2014; Lucia et al., 2014). The EPS production is highly variable and moderated by environmental factors (e.g. light,

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nutrient availability, turbidity, water flow), vertical migration cycles and biological interactions among microbial taxa (Pierre et al., 2014; Van Colen et al., 2014). Hence, it is important to highlight that macrobenthos population dynamics and spatial distribution are often linked to biofilm biomass spatial and temporal dynamics (Van Colen et al., 2012). Therefore, major biofilm functioning changes are likely to have widespread implications for aquatic ecosystem performance (Pratt et al., 2014).

Anthropogenic activities have and continue to contribute to increased erosion and consequently siltation of water systems, creating an imbalance in aquatic ecosystems (Extence et al., 2013). The effects of poor land uses on environmental imbalances (frequently

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Journal Pre-proof called environmental land use conflicts), create conflicts that are related with soil loss amplification and loss of invertebrate abundance (Pacheco et al., 2014) and diversity (Valle Junior et al., 2015). Increased sediment deposition and entrainment in aquatic ecosystems can arise from a combination of factors including discharge reduction, habitat modification, sediment erosion and direct siltation from the catchment (Donohue et al., 2003; Dalu et al., 2013; Extence et al., 2013). Arguably, the greatest contribution to altered sediment dynamics in river ecosystems is through increased terrestrial erosional processes and damming of rivers

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arising from anthropogenic activities. Globally, landscape mismanagement has resulted in

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elevated landscape erosion, increasing the sediment supply in rivers, particularly in

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developing countries (Walling, 2006; Yang et al., 2015). In addition, habitat modification of

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river ecosystems is pervasive on a global scale, with over half of the world's large river systems affected by dams (Nilsson et al., 2005). Damming has major implications for

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sediment dynamics across the axial length of rivers (Zarfl et al., 2015). Whilst the impact of

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altered sediment deposition on benthic invertebrate communities is now well recognised (e.g. Donohue et al., 2003; Jones et al., 2011; Extence et al., 2013), there is little information

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currently available on benthic algae. Macrophyte and algal community changes may not always relate directly with sediments, and in a study of a dam lake in Spain by Álvarez et al. (2017), macrophyte problems were related with uncontrolled discharges of domestic sewage. Sediment deposited within aquatic ecosystems inevitably results in an altered benthic community structure as direct (i.e. substratum smothering and interstices clogging) and indirect (e.g. macrophyte and algal community changes) effects (Parkhill and Gulliver, 2002).

Many of the effects of biofilm colonisation on different substrate types have been demonstrated on artificial structures (i.e. tiles, macrophytes, glass, bricks) (e.g. Dedić et al., 2015; Dalu et al., 2014, 2016a; Fránková et al., 2017), however, the effects of sediment

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Journal Pre-proof particle size structure remains largely unknown. To gain an improved understanding of microbial biotic interactions that drive organic matter cycling in freshwater sediments, the biogeochemical drivers of diatom carbon production needs further investigation. Much of the dissolved organic carbon in freshwater sediments consists of carbohydrate-rich EPS (McKew et al., 2013). Therefore, the present study aimed to examine to what extent total carbohydrate concentration and benthic algal biomass vary among different sediment types (size-structure categories) using a microcosm experiment conducted over a period of 28 days. We further

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aimed to investigate whether there is a relationship between benthic algal production and

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carbohydrate, and thus exopolymer concentration development. In turn, the current study

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aims to better understand the effects of substrate type on benthic algal colonisation, as it is

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critical in understanding how primary productivity will be affected by increased siltation of aquatic ecosystems under anthropogenic environmental change. In turn, we aim to decipher

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whether substrate types can determine diatom community composition, further indicating

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2. Methods

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how abiotic environmental heterogeneities can shape benthic species diversity.

2.1. Sediment processing

Sediment was collected from an open quarry (33°18'55.82"S, 26°33'33.39"E) on the Bloukrans River floodplain near the city of Grahamstown, Eastern Cape Province of South Africa and transported to a laboratory at Rhodes University Department of Zoology and Entomology for further processing. In the laboratory, sediment was dried at 60 °C for 48 hours, before being portioned into 500 g subsamples through a series of stacked sieves, agitated by a mechanical shaker (EMS-8 Electromagnetic Sieve Shaker) at a power level of 15 for 60 minutes to fractionate the sediment into five-grain sizes. The resulting five sizes (500 g) sediment classes for the experiment were: class 1 (> 500 µm), class 2 (250–500 µm),

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Journal Pre-proof class 3 (125–250 µm), class 4 (63–125 µm) and class 5 (< 63µm). The class 6 (mixed) 500 g subsample was comprised of 100 g each of size classes 1, 2, 3, 4 and 5, respectively to mimic soil structure in the natural environment. The six sediment size classes were used as the sediment treatment.

2.2. Experiment set-up and design Each sediment treatment was placed in separate 30 cm × 20 cm × 8 cm polyethylene trays

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evenly and replicated four times in a controlled environment room (25 °C, light: 12 h: day, 12

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h night) in a randomised array. Each replicate container for each treatment was then filled

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with a fixed volume of filtered (mesh size 63 µm) river water (2 L) and the initial water level

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was marked with a permanent marker. The water level was topped-up to the original level every 2 days with filtered (mesh size 63 µm) river water, to account for any loss due to

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evaporation. The experiment ran for 28 days (18 October to 15 November 2017) with

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sampling occurring every 7 days (4 replicates × 6 treatments × 4 times) for basic water parameters, benthic algal chlorophyll-a and total sediment carbohydrate concentrations.

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Additionally, dominant species counts were performed at the end of the experiment.

2.3. Sample processing

Water chemistry parameters (conductivity, pH, total dissolved solids, oxygen reduction potential (ORP) and resistivity) were measured every 7 days from all treatment replicates using a CyberScan Series 600 (Eutech Instruments, Singapore). Samples for benthic algal chlorophyll-a and carbohydrate concentration were likewise collected in each replicate every 7 days using a perspex sediment corer of 20 mm internal diameter inserted by hand into the sediment. For chlorophyll-a determination, the top 1 cm sediment layer was collected and preserved in 50 mL polyethylene containers containing 30 mL of 90 % acetone and then

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Journal Pre-proof stored in the dark for 24 hours at 4 °C. The chlorophyll-a concentrations for all replicates were measured using a Turner Designs 10-AU fluorometer (Turner Designs, San Jose) (Welschmeyer 1994; Nozais et al. 2001). Total sediment carbohydrates were measured from the collected cores using a phenol-sulfuric acid assay by adding 2 mL of distilled H2O to the collected sediment sample (i.e. 3.14 cm3), followed by 1 mL of 5 % aqueous phenol (wt/vol) and 5 mL of concentrated H2SO4. The absorbance was measured against a reagent blank at 485 nm (Dubois et al. 1956; Underwood and Paterson, 1995). Calibration was via a standard

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curve of absorption vs glucose concentration to give results in microgram (mg) glucose

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equivalents.

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At the end of the experiment (i.e. day 28), benthic algal samples were collected from the sediment surface using a syringe from all replicates (n = 4 per experimental replicate), mixed

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together to form an integrated sample for each treatment and preserved with Lugol's iodine

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solution in polyethylene containers (Taylor et al., 2005; Dalu et al., 2016b). The benthic algal groups (i.e. diatoms) were identified and enumerated using an inverted Nikon TMS light

2.4. Statistics

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microscope at ×400, according to keys by John et al. (2002) and Taylor et al. (2005).

The influence of substrate treatment (6 levels) and time (5 levels) on key water parameters (see above) was analysed using linear mixed effects models (Bates et al., 2015). For benthic algal total chlorophyll-a and total sediment carbohydrate concentrations, analyses were based on 4 time intervals (i.e. days 7, 14, 21 and 28). Further, the influence of chlorophyll-a on total sediment carbohydrate concentrations for each treatment was likewise examined using a linear mixed effects model. Here, a significant interaction term would indicate differential carbohydrate responses to chlorophyll-a among sediment treatments. To account for repeated

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Journal Pre-proof measures of each replicate over time, individual containers were included as a random effect (intercept). Diagnostic plots were examined to check model assumptions, with variables log10 transformed where necessary to improve normality and homogenise residuals. F- and t-tests via Satterthwaite’s method were used to infer the significance levels of main effects. Tukey tests via estimated marginal means were used to compute post-hoc pairwise comparisons where main effects were found to be significant (Lenth, 2018). The above statistical analyses were computed using R v3.4.2 (R Development Core Team, 2018). For diatoms, Shannon–

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Weiner diversity index, evenness and species richness were calculated in PAST version 2.0

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(Hammer et al., 2001).

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3. Results

Results of water parameter analyses are presented in Text S1. Substrate treatment and time

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had a significant effect on the total chlorophyll-a concentrations, whilst a significant

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interaction was present in the case of total sediment carbohydrates (Table 1). Total chlorophyll-a concentrations increased significantly over time (all p < 0.001), but stabilised

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between days 21 and 28 (p = 0.79). Chlorophyll-a was significantly reduced in the < 63 μm substrate treatments compared to 125–250 and 250–500 μm treatment classes overall (both p < 0.05; Fig. 1a), although treatments became more similar over time (Fig. 1a). Carbohydrate levels tended to be highest at day 7 overall, with significant undulations present over time (Fig. 1b). The significant interaction reflected emergent treatment differences among times, with the > 500 μm treatments exhibiting significantly lower total carbohydrate levels than the 63–500 treatments at day 14 (all p < 0.05; Fig. 1b). Carbohydrate differences among substrate treatments were not statistically clear on the other times (i.e. days 7, 21 and 28) (all p > 0.05).

Total sediment carbohydrates did not relate significantly to chlorophyll-a concentrations

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Journal Pre-proof overall (F1,84 = 2.04, p = 0.16), nor for any substrate treatments owing to a non-significant ‘chlorophyll-a × substrate’ interaction term (F1,84 = 0.84, p = 0.52).

Seventy-one (71) diatom species were identified at the end of the experiment, with taxa in the 63–125 μm treatment demonstrating the highest richness of 34 (Shannon-Wiener diversity index = 2.79) and the 125–250 μm treatment having the lowest at 19 (Shannon-Wiener diversity index = 2.17). The <63 μm and >500 μm treatments taxa richness were similar at

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19, but the Shannon-Wiener diversity index was 2.86 and 2.43, respectively. The 250–500

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μm and mixed sediment treatments had a taxa richness of 27 (Shannon-Wiener diversity

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index = 2.83) and 30 (Shannon-Wiener diversity index = 2.93), respectively. The dominant

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4. Discussion

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diatom species within each of the treatments are highlighted in Table 2.

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Freshwater habitats have become increasingly subjected to multiple stressors that affect their biodiversity and ecosystem functioning (Dalu et al., 2017 Romero et al., 2018; Waite et al.,

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2019; Sabater et al., 2019). Increased sedimentation and siltation associated with anthropogenic environmental change may alter microbial biofilms and the extracellular polymeric substance (EPS) they produce, with potential bottom-up effects in these ecosystems (Pratt et al., 2014). Increased sedimentation may result from hydrodynamic regime alterations associated with catchment changes, i.e. land use activities, with significant impacts on ecosystem functioning. The present study demonstrates significant effects of sediment characteristics on water parameters and chlorophyll-a concentrations, with fine sediments particularly driving reduced algal biomass, whilst significant effects on carbohydrates were subtly emergent over the monitoring period. Given that carbohydrate concentrations are known to be associated with high EPS levels (e.g., Underwood et al.,

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Journal Pre-proof 1995), it is probable that EPS was also affected by the experimental treatments. However, as the present study did not directly extract EPS, care must be taken in correlating carbohydrates with EPS as carbohydrates can also originate from other sources, such as intracellular or particle-bound materials. We also display marked differences in benthic diatom community composition according to sediment type, and therefore identify the importance of sediment characteristics for species richness. Thus, with increased sedimentation and siltation, we anticipate that the benthic algal communities, and carbohydrates that they produce, will vary

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according to substrates. In turn, this may alter benthic food webs and sediment stability.

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During the present study, the benthic algal biomass varied among the different sediment

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treatments and over time. In particular, the finest particle treatment drove significant reductions in total chlorophyll-a compared to intermediate-large particle sizes during the

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early monitoring stages. Differences in benthic algal communities and biomass were expected

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as the substrate types have different properties which drive differential nutrient retention capacities. Lane (2001), Díaz-Olarte et al. (2007), Ferragut et al. (2010) and Dalu et al.

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(2014) highlighted that the physico-chemical properties of substrates influence benthic algal species colonisation, which could explain the differences in algal species and biomass observed in the current study. However, mixed sediment treatments were not statistically different from other substrate groups in terms of algal biomass. Chlorophyll-a concentration, which is diagnostic/proxy of algal biomass/activity (Sutherland et al., 1998), increased in the sediment during the growth phase (i.e. days 7 – 21), before stabilising towards day 28. Benthic chlorophyll-a concentrations have been used as an indicator of sediment stability (Amos et al., 2004; Droppo et al., 2007); however, earlier work by Riethmüller et al. (2000) cautioned that it may not be a good indicator of sediment stability owing to site-specificity driving differences in substrate types and embeddedness. The current study indicates that the

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Journal Pre-proof finest sediment particle-size (<63 µm) may be the least stable, most likely due to lower binding, as indicated by reduced concentrations of chlorophyll-a.

The present study found that there were no significant differences in carbohydrate concentrations among the different sediment types overall, but the concentrations differed significantly over time. In turn, this may indicate non-significant effects on biofilm exopolymer concentrations by sediment types. Excluding day 7, carbohydrate concentrations

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followed a similar pattern shown by Droppo et al. (2007) when considering all substrate types

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in combination, where the concentrations generally increased over the monitoring period. In

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our study, the elevated day 7 carbohydrate concentrations may have been due to contributions

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by sediment organic matter directly, rather than diatom activity alone. A significant interaction also reflected emergent treatment differences over time. Furthermore, the present

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study found no significant relationship between total sediment carbohydrate concentrations

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and chlorophyll-a levels across sediment treatments. A major contributor to the differential carbohydrate concentrations among treatments could be different carbohydrate production

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levels of dominant diatom species that were recorded within each substrate type. Smith and Underwood (2000) and Bahulikar and Kroth (2008) have highlighted that species such as Nitzschia sigma and Navicula perminuta are, due to their large size, high carbohydrate yielding species. However, whilst the diatom community characteristics across sediment sizes varied among treatments in our study, with the dominant species existing within each treatment group generally differing, this indicated the importance of sediment type for diatom composition.

5. Conclusion While it can be concluded that sediment substrate type and species composition are important

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Journal Pre-proof for biostabilisation, attempting to unravel the biofilm, carbohydrate and stability relationship is not presently feasible in complex natural environments (Gerbersdorf and Wieprecht, 2015). Nevertheless, controlled laboratory experiments such as ours can be useful for isolating key factor effects and even interactions among factors. However, results from culture experiments such as this need to be treated with caution when interpreting findings within the context of natural settings. The present study demonstrates that sediment structure can significantly alter chlorophyll-a concentrations, with the finest particle sizes driving reduced concentrations

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compared to intermediate-large particle sizes. The effects of sediment type on carbohydrate

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levels were, statistically, less clear. However, coarsest particles exhibited significant

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reductions at certain points in time. In addition, chlorophyll-a concentrations did not relate

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significantly to carbohydrate concentrations across the experimental period, irrespective of substrate type. Thus, benthic algal biomass and activity was found to be greatest under

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coarser particle sizes, whilst carbohydrate levels, and thus possibly biofilm exopolymer

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concentrations, were relatively unaffected. We anticipate that the current study findings will lead to a better understanding of how different substrate types due to sedimentation and

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siltation will impact on primary productivity in freshwater aquatic food webs.

Acknowledgements

Financial support for this study was granted by the National Research Foundation of South Africa Thuthuka (NRF, UID: 117700) grant to TD. Any opinions, findings, conclusions or recommendations expressed in this material are those of the authors, and the NRF does not accept any liability in this regard. RNC acknowledges funding from the Department for the Economy, Northern Ireland.

Conflict of interest

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Journal Pre-proof All authors declare that no conflict of interest exists.

References Álvarez, X., Valero, E., Santos, R. M. B., Varandas, S. G. P., Sanches Fernandes, L. F. and Pacheco, F. A. L. 2017. Anthropogenic nutrients and eutrophication in multiple land use watersheds: Best management practices and policies for the protection of water resources. Land Use Policy 69: 1–11.

of

Amos, C. L., Bergamasco, A., Umgiesser, G., Cappucci, S., Cloutier, D., DeNat, L., Flindt,

ro

M., Bonardi, M. and Cristante, S. 2004. The stability of tidal flats in Venice Lagoon–the

-p

results of in–situ measurements using two benthic, annular flumes. J. Mar. Syst. 51: 211–

re

241.

Bahulikar R. A. and Kroth P. G. 2008. The complex extracellular polysaccharides of mainly

lP

chain–forming freshwater diatom species from epilithic biofilms. J. Phycol. 44: 1465–

na

1475.

Carpentier, A., Como, S., Dupuy, C., Lefrançois, C. and Feunteun, E. 2014. Feeding ecology

Jo ur

of Liza spp. in a tidal flat, evidence of the importance of the primary production (biofilm) and associated meiofauna. J. Sea Res. 92: 86–91. Cochero, J., Licursi, M. and Gómez, N. 2017. Effects of pulse and press additions of salt on biofilms of nutrient-rich streams. Sci. Total Environ. 579: 1496–1503. Dalu, T., Galloway, A. W., Richoux, N. B. and Froneman, P. W. 2016a. Effects of substrate on essential fatty acids produced by phytobenthos in an austral temperate river system. Freshwat. Sci. 35: 1189–1201. Dalu, T., Richoux, N. B. and Froneman, P. W. 2014. Using multivariate analysis and stable isotopes to assess the effects of substrate type on phytobenthos communities. Inland Waters 4: 397–412.

13

Journal Pre-proof Dalu, T., Richoux, N. B. and Froneman, P. W. 2016b. Distribution of benthic diatom communities in a permanently open temperate estuary in relation to physico–chemical variables. S. Afr. J. Bot. 107: 31–38. Dalu, T., Tambara, E. M., Clegg, B., Chari, L. D. and Nhiwatiwa, T. 2013. Modeling sedimentation rates of Malilangwe reservoir in the south–eastern lowveld of Zimbabwe. Appl. Water Sci. 3: 133–144. Dalu, T., Wasserman, R. J., Tonkin, J. D., Mwedzi, T., Magoro, M. L. and Weyl, O. L. F.

of

2017. Water or sediment? Partitioning the role of water column and sediment chemistry as

ro

drivers of macroinvertebrate communities in an austral South African stream. Sci. Total

-p

Environ 607: 317–325.

re

Dedić, A., Plenković–Moraj, A., Borojević, K. K. and Hafner, D. 2015. The first report on periphytic diatoms on artificial and natural substrate in the karstic spring Bunica, Bosnia

lP

and Herzegovina. Acta Bot. Croat. 74: 393–406.

na

Díaz–Olarte, J., Valoyes–Valois, V., Guisande, C., Torres, N. N., González–Bermúdez, A., Sanabria–Aranda, L., Hernández, A. M. M., Duque, S. R., Marciales, L. J. and Nuñez–

Jo ur

Avellaneda, M. 2007. Periphyton and phytoplankton associated with the tropical carnivorous plant Utricularia foliosa. Aquat. Bot. 87: 285–291. Donohue, I., Verheyen, E. and Irvine, K. 2003. In situ experiments on the effects of increased sediment loads on littoral rocky shore communities in Lake Tanganyika. Freshwater Biol. 48: 1603–1616. Droppo, I. G., Ross, N., Skafel, M. and Liss, S. N. 2007. Biostabilization of cohesive sediment beds in a freshwater wave‐ dominated environment. Limnol. Oceanogr. 52: 577– 589. Dubois, M., Gilles, K. A., Hamilton, J. K., Rebers, P. T. and Smith, F. 1956. Colorimetric method for determination of sugars and related substances. Analyt. Chem. 28: 350–356.

14

Journal Pre-proof Extence, C., Chadd, P. R., England, J., Dunbar, J. M., Wood, J. P. and Taylor, D. E. 2013. The assessment of fine sediment accumulation in rivers using macro‐ invertebrate community response. River Res. Appl. 29: 17–55. Fránková, M., Šumberová, K., Potužák, J. and Vild, O. 2017. The role of plant substrate type in shaping the composition and diversity of epiphytic diatom assemblages in a eutrophic reservoir. Fund. Appl. Limnol. 189: 117–135. Gerbersdorf, S. U. and Wieprecht, S. 2015. Biostabilization of cohesive sediments: revisiting

ro

and biofilm architecture. Geobiology 13: 68–97.

of

the role of abiotic conditions, physiology and diversity of microbes, polymeric secretion,

-p

Hammer, O., Harper, D. A. T. and Ryan, P. D. 2001. PAST: Paleontological Statistics

re

software for education and data analysis. Palaeontol. Electron. 4: 9. John, D., Whitton, B., Brook, A. (eds). 2002. The Freshwater Algal Flora of the British Isles:

lP

An Identification Guide to Freshwater and Terrestrial Algae. Cambridge University Press,

na

Cambridge.

Jones, J. I., Murphy, J. F., Collins, A. L., Sear, D. A., Naden, P. S. and Armitage, P. D. 2012.

Jo ur

The impact of fine sediment on macro‐ invertebrates. River Res. Appl. 28: 1055–1071. Ferragut, C., Rodello, A. F. and de Mattos Bicudo, C. E. 2010. Seasonal variability of periphyton nutrient status and biomass on artificial and natural substrates in a tropical mesotrophic reservoir. Acta Limnol. Bras. 22: 397–409. Lane, C. M. 2001. A comparison of diatom assemblages in two adjacent coastal dune lakes, northern New South Wales. Quat. Aust. 19: 34–42. Lucia, M., Bocher, P., Chambosse, M., Delaporte, P. and Bustamante, P. 2014. Trace element accumulation in relation to trophic niches of shorebirds using intertidal mudflats. J. Sea Res. 92: 134–143. McCune, B. and Mefford, M. J. 2006. PC–ORD:Multivariate Analysis of Ecological Data.

15

Journal Pre-proof Version 5.10. MjM Software, Gleneden Beach, Oregon, USA. McKew, B. A., Dumbrell, A. J., Taylor, J. D., McGenity, T. J. and Underwood, G. C. J. 2013. Differences between aerobic and anaerobic degradation of microphytobenthic biofilmderived organic matter within intertidal sediments. FEMS Microbiol. Ecol. 84: 495–509. Nilsson, C., Reidy, C. A., Dynesius, M. and Revenga, C. 2005. Fragmentation and flow regulation of the world's large river systems. Science 308: 405–408. Nozais, C., Perissinotto, R. and Mundree, S. 2001. Annual cycle of microalgal biomass in a

of

South African temporarily–open estuary: nutrient versus light limitation. Mar. Ecol. Progr.

ro

Ser. 223: 39–48.

-p

Orvain, F., De Crignis, M., Guizien, K., Lefebvre, S., Mallet, C., Takahashi, E. and Dupuy,

re

C. 2014. Tidal and seasonal effects on the short–term temporal patterns of bacteria,

Sea Res. 92: 6–18.

lP

microphytobenthos and exopolymers in natural intertidal biofilms (Brouage, France). J.

na

Pacheco, F. A. L., Varandas, S. G. P., Sanches Fernandes, L. F. and Valle Junior, R. F. 2014. Soil losses in rural watersheds with environmental land use conflicts. Sci. Total Environ.

Jo ur

485–486: 110–120.

Parkhill, K. L. and Gulliver, J. S. 2002. Effect of inorganic sediment on whole stream productivity. Hydrobiologia 472: 5–17. Pierre, G., Zhao, J. M., Orvain, F., Dupuy, C., Klein, G., Graber, M. and Maugard, T. 2014. Seasonal dynamics of extracellular polymeric substances (EPS) in surface sediments of a diatom-dominated intertidal mudflat (Marennes-Oléron, France). J. Sea Res. 92: 26–35. Porej, D. and Hetherington, T. E. 2005. Designing wetlands for amphibians: the importance of predatory fish and shallow littoral zones in structuring of amphibian communities. Wetlands Ecol. Manage, 13: 445–455. Pratt, D. R., Pilditch, C. A., Lohrer, A. M. and Thrush, S. F. 2014. The effects of short–term

16

Journal Pre-proof increases in turbidity on sandflat microphytobenthic productivity and nutrient fluxes. J. Sea Res. 92: 170–177. Riethmüller, R., Heineke, M., Kühl, H. and Keuker–Rüdiger, R. 2000. Chlorophyll a concentration as an index of sediment surface stabilisation by microphytobenthos? Cont. Shelf Res. 20: 1351–1372. Romero, F., Sabater, S., Timoner, X. and Acuña, V. 2018. Multistressor effects on river biofilms under global change conditions. Sci. Total Environ. 627: 1–10.

of

Sabater, S., Elosegi, A. and Ludwig, R. (eds). 2019. Multiple Stressors in River Ecosystems:

ro

Status, Impacts and Prospects for the Future. Elsevier, Amsterdam.

-p

Smith, D. J. and Underwood, G. J. C. 2000. The production of extracellular carbohydrates by

re

estuarine benthic diatoms: the effects of growth phase and light and dark treatment. J. Phycol. 36: 321–333.

lP

Sutherland, T. F., Amos, C. L. and Grant, J. 1998. The effect of buoyant biofilms on the

Oceanogr. 43: 225–235.

na

erodibility of sublittoral sediments of a temperate microtidal estuary. Limnol.

Jo ur

Takahashi, E., Ledauphin, J., Goux, D. and Orvain, F. 2010. Optimising extraction of extracellular polymeric substances (EPS) from benthic diatoms: comparison of the efficiency of six EPS extraction methods. Mar. Freshwat. Res. 60: 1201–1210. Taylor, J. C., Harding, W. R. and Archibald, C. G. M. 2007. An illustrated guide to some common diatom species from South Africa. WRC Report TT 282/07. Water Research Commission, Pretoria. Underwood, G. J. and Paterson, D. M. 2003. The importance of extracellular carbohydrate productionby marine epipelic diatoms. Adv. Bot. Res. 40: 183–240. Underwood, G. J. C., Paterson, D. M. and Parkes, R. J. 1995. The measurement of microbial carbohydrate exopolymers from intertidal sediments. Limnol. Oceanogr. 40: 1243–1253.

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Journal Pre-proof Valle Junior, R. F., Varandas, S. G. P., Pacheco, F. A. L., Pereira, V. R., Santos, C. F., Cortes, R. M. V. and Fernandes, L. F. S. 2015. Impacts of land use conflicts on riverine ecosystems. Land Use Policy 43: 48–62. Van Colen, C., Rossi, F., Montserrat, F., Andersson, M. A., Gribsholdt, B., Herman, P. M. J., Degraer, S., Vincx, M., Ysebaert, T. and Middelburg, J. J. 2012. Organism–sediment interactions govern post–hypoxia recovery of ecosystem functioning. PLoS One 7: e49795.

of

Van Colen, C., Underwood, G. J., Serôdio, J. and Paterson, D. M. 2014. Ecology of intertidal

ro

microbial biofilms: Mechanisms, patterns and future research needs. J. Sea Res. 92: 2–5.

-p

Waite, I. R., Munn, M. D., Moran, P. W., Konrad, C. P., Nowell, L. H., Meador, M. R., Van

re

Metre, P. C. and Carlisle, D. M. 2019. Effects of urban multi–stressors on three stream biotic assemblages. Sci. Total Environ. 660: 1472–1485.

na

Geomorphology 79: 192–216.

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Walling, D. E. 2006. Human impact on land–ocean sediment transfer by the world’s rivers.

Wang, H., Wang, W., Yin, C., Wang, Y. and Lu, J. 2006. Littoral zones as the “hotspots” of

5522–5527.

Jo ur

nitrous oxide (N2O) emission in a hyper–eutrophic lake in China. Atmos. Environ. 40:

Welschmeyer, N. A. 1994. Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and phaeopigments. Limnol. Oceanogr. 39: 1985–1992. Xu, H., Yu, G. and Jiang, H. 2013. Investigation on extracellular polymeric substances from mucilaginous cyanobacterial blooms in eutrophic freshwater lakes. Chemosphere 93: 75– 81. Yang, S. L., Xu, K. H., Milliman, J. D., Yang, H. F. and Wu, C. S. 2015. Decline of Yangtze River water and sediment discharge: Impact from natural and anthropogenic changes. Sci. Reports 5: 12581.

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Journal Pre-proof Yallop, M. L., Paterson, D. M. and Wellsbury, P. 2000. Interrelationships between rates of microbial production, exopolymer production, microbial biomass, and sediment stability in biofilms of intertidal sediments. Microbial Ecol. 39: 116–127. Zarfl, C., Lumsdon, A. E., Berlekamp, J., Tydecks, L. and Tockner, K. 2015. A global boom

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in hydropower dam construction. Aquat. Sci. 77: 161–170.

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List of Figures

Fig. 1. Concentrations of: (a) benthic algal chlorophyll–a and (b) total sediment carbohydrate (glucose equivalents) measured over the duration of the experimental study

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Journal Pre-proof List of Tables Table 1. Linear mixed effects model results considering key parameters as a function of substrate treatment and week, and their interaction. Significant p–values are emboldened. p–value 0.004 < 0.001 0.68 0.39 < 0.001 0.02

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F–value 5.26 60.06 0.79 1.06 27.69 2.04

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Carbohydrates

Predictor Substrate Week Substrate × Week Substrate Week Substrate × Week

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Parameter Chlorophyll–a

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Journal Pre-proof Table 2. Dominant relative abundances (> 5 %) of diatom taxa identified among the different substrate types collected on day 28. %

63–125

%

125–250

%

Melosira varians

10.2

Staurosira elliptica

15.5

Amphora coffeaeformis

40.2

Navicula veneta

8.9

Navicula sp.

13.3

Amphora copulata

12.7

Navicula cryptocephala

8.0

Nitzschia filiformis

13.1

Nitzschia liebertruthii

6.6

Surirella sp.

8.0

Gomphonema lagenula

10.3

Nitzschia pura

6.6

Fragilaria ulna var. acus

7.6

Gomphonema venusta

10.1

Staurosira elliptica

6.0

Gyrosigma sp.

6.7

Nitzschia linearis

5.2

Nitzschia sigma

5.8

Nitzschia gracilis

6.7

Suriella ovalis

6.7

Diploneis sp.

5.3

Navicula gregaria

5.3

250–500

%

Navicula trivalis

13.1

Navicula zanonii

Navicula cryptocephala

12.7

Nitzschia sp. 3

Nitzschia linearis

9.8

Nitzschia palea

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< 63

Mixed

%

28.8

Amphora pediculus

10.8

14.4

Gomphonema venusta

10.8

Nitzschia communis

7.7

Navicula riediana

10.1

9.0

Fragilaria sp.

6.9

Gomphonema lagenula

8.6

Nitzschia obtusa var. kutzii

7.2

Nitzschia sp. 4

6.9

Nitzschia linearis

8.2

Navicula riediana

6.7

Nitzschia sp. 1

6.7

Navicula cryptotonella

7.7

Cyclotella meneghianana

5.1

Gomphonema affine

6.4

Navicula sp.

7.4

Hantzschia amphioxys

5.1

Amphora copulata

5.5

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%

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> 500

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Highlights

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Graphical abstract



Substrate treatment and time had significant effect on total chlorophyll-a.



Carbohydrate differences among substrate treatments were not statistically clear.



Total sediment carbohydrates did not relate significantly to chlorophyll-a.



Benthic algal biomass and activity was found to be greatest under coarser particle sizes.

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