Comparing two periphyton collection methods commonly used for stream bioassessment and the development of numeric nutrient standards

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 0.2 mg 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 (4.4-57.9 mg m^-2 ) with increasing P concentrations (p < .001) after P enrichment but was threefold greater after N+P enrichment, increasing from 13.3 to 171.1 mg 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.

Temporal Effects of Groundwater on Physical and Biotic Components of a Karst Stream

Although most lotic ecosystems are groundwater dependent, our knowledge on the relatively long-term ecological effects of groundwater discharge on downstream reaches remains limited. We surveyed four connected reaches of a Chinese karst stream network for 72 consecutive months, with one reach, named Hong Shi Zi (HSZ), evidently affected by groundwater. We tested whether, compared with other reaches, HSZ had (1) milder water temperature and flow regimes, and (2) weaker influences of water temperature and flow on benthic algal biomass represented by chlorophyll a (Chl. a) concentrations. We found that the maximum monthly mean water temperature in HSZ was 0.6 °C lower than of the adjacent upstream reach, and the minimum monthly mean water temperature was 1.0 °C higher than of the adjacent downstream reach. HSZ had the smallest coefficient of variation (CV) for water temperature but the largest CV for discharge. Water temperature and discharge displayed a significant 12-month periodicity in all reaches not directly groundwater influenced. Only water temperature displayed such periodicity in HSZ. Water temperature was an important predictor of temporal variation in Chl. a in all reaches, but its influence was weakest in HSZ. Our findings demonstrate that longer survey data can provide insight into groundwater–surface water interactions.