Effects of upstream lakes and nutrient limitation on periphytic biomass and nitrogen fixation in oligotrophic, subalpine streams

Abstract

Summary 1. We conducted bioassays of nutrient limitation to understand how macronutrients and the position of streams relative to lakes control nitrogen (N2) fixation and periphytic biomass in three oligotrophic Rocky Mountain catchments. We measured periphytic chlorophyll‐a (chl‐a) and nitrogen‐fixation responses to nitrogen (N) and phosphorus (P) additions using nutrient‐diffusing substrata at 19 stream study sites, located above and below lakes within the study catchments. 2. We found that periphytic chl‐a was significantly co‐limited by N and P at 13 of the 19 sites, with sole limitation by P observed at another four sites, and no nutrient response at the final two sites. On average, the addition of N, P and N + P stimulated chl‐a 35%, 114% and 700% above control values respectively. The addition of P alone stimulated nitrogen fixation by 2500% at five of the 19 sites. The addition of N, either with or without simultaneous P addition, suppressed nitrogen fixation by 73% at nine of the 19 sites. 3. Lake outlet streams were warmer and had higher dissolved organic carbon concentrations than inlet streams and those further upstream, but position relative to lakes did not affect chl‐a and nitrogen fixation in the absence of nutrient additions. Chl‐a response to nutrient additions did not change along the length of the study streams, but nitrogen fixation was suppressed more strongly by N, and stimulated more strongly by P, at lower altitude sites. The responses of chl‐a and nitrogen fixation to nutrients were not affected by location relative to lakes. Some variation in responses to nutrients could be explained by nitrate and/or total N concentration. 4. Periphytic chl‐a and nitrogen fixation were affected by nutrient supply, but responses to nutrients were independent of stream position in the landscape relative to lakes. Understanding interactions between nutrient supply, nitrogen fixation and chl‐a may help predict periphytic responses to future perturbations of oligotrophic streams, such as the deposition of atmospheric N.

Nutrient additions to mitigate for loss of Pacific salmon: consequences for stream biofilm and nutrient dynamics

“…Nutrient limitation.-Nutrient limitation of biofilms was determined following treatment application in 2008 using nutrient diffusing substrates (NDS; Tank et al 2006, Marcarelli andWurtsbaugh 2007). Plastic vials measuring 37-mL were filled with nutrient-enriched 2% agar and capped with a 2.6-cm diameter fritted glass disk (Leco, St. Joseph, Michigan, USA).…”

“…The decline of Pacific salmon has fueled concern about declining ecosystem productivity, termed oligotrophication, following loss of material and nutrient subsidies (Stockner et al 2000). For example, in the headwaters of the Snake and Salmon Rivers in central Idaho, dramatic declines in salmon returns (McClure et al 2003) and continued outmigration of juvenile fish (Scheuerell et al 2005, Kohler et al 2013, coupled with extremely low geologic, atmospheric, and anthropogenic nutrient sources, have been linked to very low background nutrient concentrations and consistent nutrient limitation of stream biofilms (Thomas et al 2003, Marcarelli and Wurtsbaugh 2007, Sanderson et al 2009). There is concern that reduced nutrient returns have led to decreases in primary and secondary production, in turn causing bottom-up limitation of juvenile salmon production.…”

Controls of Benthic Nitrogen Fixation and Primary Production from Nutrient Enrichment of Oligotrophic, Arctic Lakes

“…Filamentous autotrophic N 2 fixers may also require a source of inorganic N to stimulate photosynthesis and carbon transfer from the photosynthetic cells to the heterocyst (Vitousek and Howarth 1991). others (2004, 2006) showed that a sufficient energy supply is needed from photosynthetic cells before N 2 fixation can occur, and this phenomenon could be evidenced by the fact that some nutrient addition experiments in oligotrophic systems have shown an inconsistent response of N 2 fixation to added N and P (for example, Marcarelli and Wurtsbaugh 2007). The idea that N or P may limit N 2 fixation in very oligotrophic systems has not been well evaluated but may help explain why compensatory N 2 fixation Although benthic processes are generally more important in oligotrophic systems than in more enriched systems, the response of benthic processes to nutrient enrichment is in part dependent upon lake geomorphology (Vadeboncoeur and others 2008).…”

Fluvial lakes affect on phosphorus and potassium concentrations in the Samica Stęszewska River

“…2000;Neal et al 2008). However, these differences are not always sharp and, still, it is unclear how natural lakes are ecologically linked with their inlet and outlet rivers (Hillbricht-Ilkowska 1999;Marcarelli and Wurtsbaugh 2007). This interaction may have differentiated strength and might change, for example, due to the modification of nutrient availability (Kling et al 2000), hydrology or morphology (Arp et al 2006).…”

“…Flow rivers have significant positive or negative influence on lake ecosystem or inversely, these ecosystems may also impact flow rivers (Hillbricht-Ilkowska 1999;Marcarelli and Wurtsbaugh 2007). Lakes, in relations to streams, have longer hydraulic retention times and, are characterised by domination of sedimentation and accumulation processes over erosion as well as advantage of autochthonous material over allochthonous, etc.…”