Periphyton Biomass In Streams Research Articles

Influence of riparian thinning on trophic pathways supporting stream food webs in forested watersheds

AbstractResource managers seek to thin second‐growth riparian forests to address multiple stream and riparian management objectives, including enhancing aquatic productivity via light‐mediated trophic pathways in watersheds of the Pacific Northwest (USA). However, such increases in aquatic productivity depend on complex food web dynamics that link riparian forests and streams. To evaluate how riparian forest thinning influences stream food webs, we conducted a replicated, manipulative field experiment in three northern California watersheds composed of second‐growth redwood forests and tracked responses across multiple trophic levels (periphyton, macroinvertebrates, amphibians, and fish) 1 year pre‐ and post‐treatment. Riparian thinning treatments increased light to the stream channel, yet we observed mixed responses by stream food webs. Thinning did not change stream periphyton biomass on natural substrates but increased periphyton accrual on ceramic tiles. Periphyton accrual appeared to be partially muted by top‐down effects from invertebrate scrapers, which were more abundant in thinned reaches. Prey in the diets of top predators—coastal giant salamanders (Dicamptodon tenebrosus) and coastal cutthroat trout (Oncorhynchus clarkii clarkii)—did not change in biomass, composition, or structure in response to thinning and instead varied more seasonally and between predators. Stable isotope analysis indicated that shifts in carbon (δ13C) signatures of stream periphyton associated with thinning were reflected to varying extents by primary consumers but did not propagate up to top predators. Top predator biomass responses varied between species, where salamander biomass remained unchanged, but cutthroat trout biomass increased slightly in thinned reaches. However, trout biomass responses were not supported by diets or isotopes and correlated weakly with changes in light associated with thinning, suggesting little evidence that responses could be attributed directly to changes in autotrophic pathways. Furthermore, we found no evidence that local trophic responses to thinning propagated into downstream reaches. Taken together, we observed that trophic pathways supporting stream food webs remained largely intact immediately after riparian thinning treatments. Collectively, these results suggest that riparian thinning does not necessarily enhance aquatic productivity in forested streams, indicating that contextual factors driving realized ecological responses should be accounted for when considering thinning as a restoration strategy for stream–riparian ecosystems.

Watershed farmland area and instream water quality co-determine the stream primary producer in the central Hengduan Mountains, southwestern China

As the main primary producer in stream ecosystems, periphyton is the fundamental of stream ecosystems and plays an essential role in maintaining stream biodiversity. The central Hengduan Mountains is one of the famous global biodiversity hotspots. However, for stream biodiversity conservations, the fundamental information about the spatial pattern of stream periphyton and the determining factors in this region remains largely unknown. To fill this gap, we investigated the spatial pattern of periphyton biomass (measured by chlorophyll a) in four typical streams in the central Hengduan Mountains and analyzed the driving factors, with the perspective of watershed land use and instream water quality. The results of our study found that farmland area, instream dissolved silicate (DSi), and water temperature (WT) had significant negative relationships with the stream periphyton biomass in the central Hengduan Mountains. However, the dissolved inorganic phosphorus (DIP) and dissolved inorganic nitrogen (DIN) had non-significant effects on the periphyton biomass in our study. Further analysis showed that the correlation between the ratio of farmland in the catchment and the DSi is non-significant (r = 0.028, P = 0.698), suggesting that the changes in farmland area will not affect the concentration of dissolved silicate in the stream. This reveals that the stream periphyton biomass was co-determined by the watershed farmland area and instream DSi and WT, but not nitrogen or phosphorus. These results highlight the importance of farmland management and instream DSi for stream ecosystems in the central Hengduan Mountains. Our study investigated the spatial pattern of the stream primary producer in the central Hengduan Mountains region and identified the main determining factors, which could improve our understanding of the high mountain stream ecosystems.

Consequences of a terrestrial insect invader on stream-riparian food webs of the central Appalachians, USA

The terrestrial invader hemlock woolly adelgid (Adelges tsugae) decimates eastern hemlock (Tsuga canadensis) stands that dominate riparian zones of Appalachian forest streams. However, the ecological consequences for linked aquatic-terrestrial ecosystems remain unknown. We measured stream-riparian trophic linkages at 21 sites of Ohio, West Virginia, and Virginia representing a chronosequence of T. canadensis decline. We measured reciprocal fluxes of basal resources (periphyton, terrestrial detritus), emerging aquatic insect flux rate and community composition, riparian orb-weaving spider density, and estimated spider trophic position and reliance on aquatically-derived energy using stable isotopes (13C, 15N, 2H) and Bayesian mixing models. Stream periphyton biomass was greater at uninvaded reference sites than at invaded sites and composition of the terrestrial-to-stream detritus flux changed with T. canadensis decline. Emergent aquatic insect community composition was partly explained by hemlock decline status, but the relative abundance of functional feeding groups was not. Riparian orb-weaving spider densities were highest at sites with severe hemlock decline (F = 4.27, p = 0.022), but were not linked to insect emergence flux rates (p > 0.10). Both trophic position ( $${\overline{x}}$$ = 2.4) and relative reliance on aquatically-derived energy ( $${\overline{x}}$$ = 83%) were comparable among spider families (Tetragnathidae, Araneidae, Pisauridae) and site decline status. Although spider δ13C signatures were unrelated to those of the most numerous emergent insect families, δ15N signatures of Araneidae and Pisauridae tracked emergent insect δ15N (r2 = 0.42 and 0.78, respectively), suggesting a trophic linkage. Overall, the ecological consequences of this invader were clearest at lower trophic levels, with more nuanced impacts on riparian spiders.

Stream algal biomass response to experimental phosphorus and nitrogen gradients: A case for dual nutrient management in agricultural watersheds.

Watershed managers generally focus on P reduction strategies to combat freshwater eutrophication despite evidence that N co-limits primary production. Our objective was to test the role of P in limiting stream periphyton biomass within the Buffalo River watershed in Arkansas by conducting a 31-d streamside mesocosm experiment. To represent potentially different starting states, cobbles were transplanted from two different tributary streams and initially exposed to a range of P (0, 0.012, 0.025, 0.05, 0.1, and 0.2mg L-1 P) to assess benthic ash-free dry mass (AFDM) and chlorophyll-a (chl a) and responses during a P only enrichment period. Later, the experiment was continued under a N/P (10:1 molar ratio) enrichment gradient to examine co-limitation. Mean AFDM was higher on Day 31 of the N+P enrichment compared with Day 17 of the P-only enrichment (p<.001). Overall differences in AFDM and chl a were observed between cobbles from different stream sites. Phosphorus enrichment stimulated benthic chl a biomass, but enrichment effects were greater when streams were enriched with N+P (p<.001). Chlorophyll-a increased (4.4-57.9mg m-2 ) with increasing P concentrations (p<.001) after P enrichment but was threefold greater after N+P enrichment, increasing from 13.3 to 171.1mg m-2 across the enrichment gradient. Results support the need to consider both N and P limitation in freshwater systems and demonstrate that potential increases in nutrient concentrations may influence accumulation of algae on cobble substrates from the Buffalo River watershed.

Effects of eutrophication on maximum algal biomass in lake and river ecosystems

To further clarify empirical relationships between maximum phytoplankton biomass per unit total phosphorus (TP) and the maximum:mean phytoplankton biomass ratio, predictive models were created from a meta-analysis of datasets from lakes worldwide. Peak concentrations of planktonic chlorophyll a were on average 2.6 times greater than the mean, with most maximum:mean chlorophyll a ratios falling within less than an order-of-magnitude band (from 1.2 to 6 times the mean value). Peak concentrations of planktonic algal biovolume in 22 Organisation for Economic Co-operation and Development (OECD) lakes were on average 3.3 times greater than the mean, with maximum:mean biovolume ratios ranging from 1.2 to 6.3. By contrast, the temporal dynamics of planktonic (suspended) algal biomass in Minnesota streams and rivers were far more constrained; peak concentrations of planktonic chlorophyll a were only on average 1.8 times greater than the mean, with maximum:mean chlorophyll a ratios ranging from 1.3 to 3.8. These data suggest regional differences in maximum chlorophyll a values may exist. Parallel analyses of periphyton biomass in streams and rivers showed far greater variability in the maximum:mean chlorophyll ratio for benthic algae. Peak concentrations of attached chlorophyll a were on average 4.3 times greater than the mean, with the observed maximum:mean chlorophyll a ratios exhibiting exceptionally high variability (ranging from 1.0 to 50 times the mean value), likely reflecting differences in the temporal dynamics of planktonic and benthic algal growth in freshwater ecosystems.

Altitudinal pattern of stream periphyton biomass in tributaries of the Lancang–Mekong River: An indicator of anthropogenic impact?

As the primary producer in streams, periphyton plays an important ecological role in nutrient cycling processes, and has been widely used as an indicator for stream assessment and management. This study examined altitudinal patterns of stream periphyton biomass and their relations to environmental variables in three tributaries of the Lancang–Mekong River. Total dissolved solids, conductivity, and water temperature related negatively with elevation in the three streams. Periphyton biomass showed distinct responses to environmental variables in three streams, and no environmental variables had significant relationship with periphyton biomass in all streams. Altitudinal patterns of periphyton biomass in three streams were uniform: it had a positive relation with elevation, showing a consistent trend with the anthropogenic impact. The altitudinal pattern of stream periphyton biomass could be an ideal indicator to assess stream ecological condition, and monitor anthropogenic impact on mountain streams in the Lancang–Mekong River system.

Fish determine macroinvertebrate food webs and assemblage structure in Greenland subarctic streams

Summary Climate warming in (sub)arctic regions is expected to increase freshwater fish overwinter survival and dispersal, potentially with strong implications for macroinvertebrate assemblage composition and ecosystem processes. Several studies worldwide have shown large effects of top predators (usually fish) on macroinvertebrates in streams. However, the influence of top predators on trophic diversity, the range of food resources exploited and trophic niche redundancy is less well studied, particularly in cold regions. Using stable isotopes (13C and 15N) and fish gut content analysis, we investigated the effect of top predators on macroinvertebrate food webs in streams in Greenland by comparing adjacent sites with and without fish (Gasterosteus aculeatus). Food‐web metrics estimated from stable isotope data showed that the presence of fish reduced the diversity of food sources exploited by macroinvertebrates as well as their trophic diversity. In addition, fish presence increased packing and trophic redundancy of macroinvertebrate taxa in the food web, possibly due to behavioural changes in foraging activity. Furthermore, predatory macroinvertebrate taxa were unable to attain the trophic position of fish so that food webs were one trophic level longer in streams with fish. Focusing on macroinvertebrate food webs alone, predatory macroinvertebrates did not change their trophic position in the presence of fish. Filter feeders dominated the macroinvertebrate assemblage when fish were present, while the relative abundance of collector‐gatherers was marginally higher in the fishless streams. This pattern was consistent with stronger selectivity for collector‐gatherers by fish. Climate‐driven fish colonisation in currently fishless Greenland streams may induce a shift in macroinvertebrate food webs, with a reduction in both trophic diversity and the variety of food sources consumed. To some extent, this might counteract a change towards a broader use of food resources by macroinvertebrates that might otherwise be expected at higher temperatures. In addition, a shift in the macroinvertebrate assemblage towards dominance of filter feeders can be expected to promote an increase in periphyton biomass in streams with fish.

Longitudinal patterns of periphyton biomass in Qinghai–Tibetan Plateau streams: An indicator of pasture degradation?

Periphyton communities play a key role in stream ecosystems, and are usually used as an indicator for long-term biological monitoring, management and evaluation. This study examined the relationships between environmental variables and stream periphyton biomass, investigated the longitudinal patterns of periphyton biomass, and explored the relationships between these longitudinal patterns and pasture degradations in Qinghai–Tibetan Plateau. Isolated environmental variables did not have significant impacts on periphyton biomass and did not clearly respond to the influence of pasture degradation. The longitudinal patterns of stream periphyton biomass were consistent with pasture degradation trends. The more serious the pasture degradation, the lower is the periphyton biomass. Longitudinal gradient is a comprehensive variable, which represents a number of space-related environmental factors. In Qinghai–Tibetan Plateau, the pasture ecosystems are fragile and have been severely degraded. The longitudinal patterns of periphyton biomass were closely related to ecological degradation and can be used as an indicator to monitor and evaluate pasture degradation in Qinghai–Tibetan Plateau.

Elevated light and nutrients alter the nutritional quality of stream periphyton

Summary The biochemical composition of primary food resources may affect secondary production, growth, reproduction and other physiological responses in consumers and may be an important driver of food‐web dynamics. Changes in land use, riparian clearing and non‐point nutrient inputs to streams have the potential to alter the biochemical composition of periphyton, and characterising this relationship may be critical to understand the processes by which environmental change can affect food webs and ecosystem function. We conducted a manipulative, in situ experiment to examine the effect of light and nutrient availability on stream periphyton biomass, nutrient content, stoichiometry and fatty acid composition. Greater light increased periphyton biomass [chl‐a, ash‐free dry mass (AFDM)], periphyton carbon concentrations and monounsaturated fatty acids (MUFAs), but decreased saturated fatty acids (SAFAs). Greater light availability also increased levels of &lt;20C polyunsaturated fatty acids (PUFAs), but decreased quantities of several long‐chain (20–22 C), highly unsaturated fatty acids (HUFAs). Nutrient (+N, +P) addition had no significant effect on periphyton biomass in the study streams, but did increase periphyton carbon content. For fatty acids, despite non‐significant effects on periphyton biomass, nutrient additions resulted in an increased ratio of SAFA to PUFA, greater concentrations of stearidonic acid (18:4ω3) and near‐significant increases in α‐linolenic acid (18:3ω3). Nutrient additions also resulted in decreased quantities of the physiologically important docosahexaenoic acid (DHA; 22:6ω3) and increased the ratio of omega‐3 to omega‐6 fatty acids. An interaction between nutrient addition and greater light also resulted in decreased percentages of another physiologically important fatty acid, eicosapentaenoic acid (EPA; 20:5ω3). Results from this study suggest that increased light and nutrients, a condition common in urban and agricultural catchments, would increase 18C PUFA intermediates that would be available in periphyton food sources, but decrease the availability of essential 20‐22C HUFAs. If stream consumers are unable to elongate PUFAs into essential HUFAs, there may be important effects on food webs, including shifts by invertebrate consumers from herbivory to omnivory or carnivory, or changes in the species composition of aquatic consumers. Our results demonstrate that fatty acid measures were more sensitive to changes in light and nutrient conditions than more traditional measures of biomass, nutrient content and stoichiometry. We recommend routine measurement of fatty acid content in monitoring the effect of changing environmental conditions in rivers and streams, particularly studies on food quality and ecosystem health.

Treated and Untreated Acid Mine Drainage Effects on Stream Periphyton Biomass, Leaf Decomposition, and Macroinvertebrate Diversity

ABSTRACT We studied the effects of acid mine drainage (AMD) on three key stream properties and functions. Four streams from each of three categories (AMD, treated AMD, and reference) were selected randomly from within the Tygart Valley River watershed in West Virginia. Analysis of stream water verified that the three stream types had very distinct chemical characteristics. Periphyton biomass was significantly reduced in AMD streams; however, treated AMD streams were no different from reference streams. Leaf decomposition was significantly slower in treated streams than in reference streams. Compared to reference streams AMD streams exhibited significantly lower macroinvertebrate density and diversity, whereas treated AMD streams had lower diversity. Thus, although treated AMD is much less toxic than raw AMD, it still has substantial impacts on macroinvertebrate diversity and leaf decomposition which could lead to ecosystem-wide impacts.

Resource Stress Alters Hydrological Disturbance Effects in a Stream periphyton Community

Scouring reduces stream periphyton biomass during floods, and levels of light and nutrient resource supply can influence growth and community physiology between floods. We hypothesised that for a given taxonomic structure, resource stressed communities would have lower resistance and resilience to scour disturbance than resource replete communities. We investigated this in experimental streams with four combinations of light and nutrients. Communities in all treatments were dominated by similar diatoms. Resource supply significantly influenced the resistance to scouring of some components of the communities. In particular, high nutrient stress resulted in low resistance of chlorophyll a biomass (up to 94% loss), whereas moderate light stress and low nutrient stress resulted in the most resistant communities (43% loss). Resilience of chlorophyll a was negatively correlated, and resilience of taxonomic composition was positively correlated, with resource stress. In the treatments with high nutrient supply, chlorophyll a returned to pre-disturbance levels within 6 d, but regeneration of the taxonomic structure took >9 d. For the treatments with low nutrient supply, chlorophyll a took >18 d to recover, but taxonomic composition took only a few days to recover reflecting the dominance of immigration processes (and lack of in situ growth). In all treatments the scour disturbance caused a reduction in growth rates of the regenerating communities relative to the undisturbed control communities. Overall, the disturbance had a longer-term influence on community persistence under moderate to high resource stress than under low resource stress.

Microform bed clusters as refugia for periphyton in a flood‐prone headwater stream

Flood effects on benthic algal communities grown upon three common substratum types were assessed in a gravel‐bed stream. Microform bed clusters (MBCs) and, to a lesser extent, boulders conferred resistance on their associated periphyton communities (i.e., reduced flood‐induced biomass loss; functioned as refugia) relative to cobble/gravel substrata. On all substrata, flooding significantly reduced the relative abundance of Diatoma hiemale, and increased the relative abundance of Gomphonema minutum f. syriacum and/or Ampithrix sp. Long‐term (>4 months) sampling indicated that MBCs generally supported more algal biomass than did boulders, which, in turn, supported greater biomass than cobbles/gravels. Manipulation of the abundance of refugial structures (e.g., MBCs) could possibly alter productivity of flood‐prone gravel‐bed streams. Stream periphyton biomass models may be improved by explicit consideration of the effects of refugial substrata. The interstitial spaces of MBCs may constitute a unique habitat, and deserve further study.

Developing nutrient targets to control benthic chlorophyll levels in streams: A case study of the Clark Fork River

Approaches for assessing the effects of lowering nutrients on periphyton biomass in streams and rivers are poorly developed in contrast to those for lakes. Here we present two complementary approaches to assess target nutrient concentrations in streams, given desired mean and maximum standing crops of benthic algal chlorophyll. In the first approach, a reference portion or reach of the river that typically exhibits acceptable levels of benthic chlorophyll is identified (i.e. seasonal mean and maximum values do not exceed desirable levels), and the target levels for instream nutrient concentrations are defined by mean nutrient levels in the reference region. In the second approach, regression and graphical analysis of a large stream database are used to identify acceptable levels of instream total N and total P. The first approach supplies site-specific nutrient targets, whereas the second places nutrient control into a broader, more comparative perspective. In order to link these target concentrations to specific nutrient control measures, we describe a spreadsheet model that can be used to translate changes in external loading by point sources into predicted new instream nutrient concentrations. These quantitative methods are applied here to the control of nuisance algal growth in the Clark Fork River, Montana. We suggest that, in general, maintenance of mean instream total N concentrations below 350 μg l −1 and total P below 30 μg l −1 will result in mean benthic algal chlorophyll a density below nuisance levels of 100 mg m −2 in most streams.