▪ Abstract Animals are important in nutrient cycling in freshwater ecosystems. Via excretory processes, animals can supply nutrients (nitrogen and phosphorus) at rates comparable to major nutrient sources, and nutrient cycling by animals can support a substantial proportion of the nutrient demands of primary producers. In addition, animals may exert strong impacts on the species composition of primary producers via effects on nutrient supply rates and ratios. Animals can either recycle nutrients within a habitat, or translocate nutrients across habitats or ecosystems. Nutrient translocation by relatively large animals may be particularly important for stimulating new primary production and for increasing nutrient standing stocks in recipient habitats. Animals also have numerous indirect effects on nutrient fluxes via effects on their prey or by modification of the physical environment. Future studies must quantify how the importance of animal-mediated nutrient cycling varies among taxa and along environme...

Nutrient Cycling by Animals in Freshwater Ecosystems

Sediment interactions with submersed macrophyte growth and community dynamics

In this paper, we report on a whole-pool manipulation of leaf litter decomposition in a tropical stream following a hurricane. The study was designed to distinguish how decapod species comprising two functional feeding guilds alter rates and magnitudes of leaf litter processing and nutrient release linking the detrital food web with the overall producer–consumer food web. Streams of the Luquillo Experimental Forest, Puerto Rico, are dominated numerically by two freshwater shrimp species (Atya lanipes and Xiphocaris elongata). To determine how these shrimp affected detrital processing following large leaf inputs associated with a hurricane, we manipulated the presence or absence of two species of shrimp in six fenced pools of a headwater stream with hurricane levels of Cecropia leaf litter over a 23-d period. The experiment was designed to determine how the two different shrimp affected: (1) the rate and amount of size fractionation of leaf material; (2) the localized nutrient concentrations in the pools; ...

https://www.jstor.org/stable/info/2680196

Freshwater shrimp effects on detrital processing and nutrients in a tropical headwater stream

The Influence of Bioturbation on Physical, Chemical and Biological Parameters in Aquatic Environments: A Review

4 – Pattern in Wetlands*

Microcosms of Lake Mendota, Wisconsin, USA sediment and oxygenated water, maintained in darkness, were used to evaluate phosphorus increments in the overlying water as influenced by 2 species of chironomids, chironomid density and chironomid-temperature interactions. Similar systems were held in light and tested with algae present to determine if the presence of chironomids enhances algal growth. Both species, Chironomous riparius and Chironomus tentans, cause increases in phosphorus content of overlying water, with the larger C. tentans producing the greater effect. Release of total phosphorus at 20?C increased approximately linearly from 0.3-9.4 mg m-2 d-1 over a range of 6 densities from 0-6585 larvae/M2. Increasing temperature from 1O-20'C had little effect on phosphorus release rates in microcosms without chironomids, but in systems with C. tentans increased temper- ature resulted in a -10-fold increase in total phosphorus release rates. Most phosphorus released to the overlying water was soluble reactive phosphorus (SRP) which was quickly taken up by algae in lighted microcosms. Lighted controls had little total phosphorus in the overlying water or on glass substrates (wall growth), while microcosms with C. tentans contained significantly more total phos- phorus in the overlying water and on glass substrates. Excretion by chironomids, rather than translocation of phosphorus from the interstitial waters of the sediment, could explain the observed data. Regardless of the mechanism, chironomids enhance phosphorus release and where abundant in the aerobic regions of lake sediments, their activities may be expected to result in a significant source of phosphorus to the epilimnetic region.

George W. Gallepp

Papers

Chironomid influence on phosphorus release in sediment-water microcosms'