N‐limited consumer growth and low nutrient regeneration N:P ratios in lakes with low N deposition

Abstract

Abstract. Nutrient limitation of primary producers and their consumers can have a large influence on ecosystem productivity. The nature and strength of nutrient limitation is driven both by external factors (e.g., nutrient loading) and internal processes (e.g., consumer-driven nutrient regeneration). Here we present results from a field study in 10 low productive headwater lakes in northern subarctic Sweden, where nitrogen (N) deposition is low and phytoplankton is primarily N-limited. We assessed the carbon:nitrogen:phosphorus (C:N:P) stoichiometry of seston and zooplankton and estimated the N:P ratio of consumer-driven nutrient regeneration. Based on stoichiometric models, the estimated elemental imbalances between seston and zooplankton suggest that zooplankton were mainly N-limited and regenerated nutrients with low N:P ratios (median 11.9, atomic ratio). The predicted N:P regeneration ratios were consistent with results from phytoplankton nutrient limitation bioassays in mid-summer, i.e., the N:P regeneration was predicted to be low when phytoplankton were N-limited, and high when phytoplankton were P-limited. During other seasons, when water discharge was high, nutrient loading from the surrounding catchments apparently had the strongest effect on phytoplankton nutrient limitation. We propose that lakes with higher N:P ratios than the open ocean is an effect of N deposition, that Nlimitation of consumers and phytoplankton is further enhanced by low nutrient regeneration N:P ratios, and that in the absence of N deposition, lake and ocean N:P stoichiometry are similar.

Cascading influences of grassland degradation on nutrient limitation in a high mountain lake and its inflow streams

“…Four treatments in triplicates were established: untreated controls (control), nitrogen addition (+N), phosphorus addition (+P), and combined nitrogen and phosphorus addition (+NP). Nutrients were added to the bottles to increase N concentrations by 100 lg/L (7.2 lmol/L) and/or P concentrations by 10 lg/L (0.3 lmol/L; Bergstrom et al 2013, Bergstr€ om et al 2015. N was added as KNO 3 and P as KH 2 PO 4 .…”

Effects of zebra mussels on cladoceran communities under eutrophic conditions

“…The N:P ratio in the tissues of cladocerans also depends on body size. Small-bodied species have been shown to have a higher percentage of nitrogen and a lower percentage of phosphorus content in their dry weight than larger daphnids (Bergström et al, 2015).…”

Pelagic food web response to whole lake N fertilization

“…In the control lakes, this threshold ratio was only exceeded on 30% of all sampling occasions in the impact years, whereas in the fertilized lakes this occurred on 68% of all occasions. Thus, although not significant, the increases in both N : P and C : P ratios after fertilization might have nevertheless been large enough to affect the development of P demanding zooplankton consumers (Sterner et al ; Elser et al ; Hessen ), forcing them to dismiss assimilated C by respiration and excretion, and N (Gliwicz ; Elser et al ; Bergström et al ). Furthermore, the increased PP : BP ratio following N fertilization indicates that increased presence of phytoplankton diluted the availability of bacteria prey which can be an important P source for especially P rich cladocerans such as Daphnia (Andersen and Hessen ).…”

“…A.) at the Limnology Department, Uppsala University, Sweden (Bergström et al ). Filters for particulate P were analyzed as for TP (cf.…”