Spatial and seasonal variation in nutrient excretion by benthic invertebrates in a eutrophic reservoir

Abstract

SUMMARY1. Nitrogen (N) and phosphorus (P) fluxes via excretion by benthic invertebrates were quantified in a eutrophic reservoir (Acton Lake, Ohio, U.S.A.). We quantified variation in nutrient fluxes seasonally (June until November 1997), spatially (three sites) and among taxa (chironomids, tubificid oligochaetes and Chaoborus). 2. The three taxa differed in spatial distribution and contribution to nutrient fluxes. Tubificids were the most abundant taxon at two oxic sites (1.5 and 4 m depth), and were exceedingly rare at an anoxic, hypolimnetic site (8 m). Chironomids were abundant only at the shallowest oxic site. Chaoborus was the only abundant taxon at the anoxic site. Total benthic invertebrate biomass was greatest at the shallowest site and lowest at the anoxic, hypolimnetic site. 3. Mass-specific excretion rate [lmol NH 4 -N or soluble reactive P (SRP) excreted mg dry mass -1 h -1 ] varied among experiments and was influenced by temperature. Differences among taxa were not significant. Thus, nutrient flux through benthic invertebrates was affected more by total invertebrate biomass and temperature than by species composition. 4. Fluxes of N and P via benthic invertebrate excretion (lmol NH 4 -N or SRP m -2 day -1 )were greatest at the oxic sites, where fluxes were dominated by the excretion of tubificids and chironomids. The N and P fluxes at the anoxic site were much lower, and were dominated by excretion by Chaoborus. The ratio of N and P excreted by the benthic invertebrate assemblage varied seasonally and was lowest at the anoxic site. 5.Comparison with other measured inputs shows that excretion by benthic invertebrates could be an important source of nutrients, especially of P. However, the relative importance of nutrient excretion by the benthos varies greatly spatially and temporally.

Phosphorus flux by macrobenthic invertebrates in a shallow eutrophic lake Donghu: spatial change

“…Zoobenthos (chironomids and oligochaetes) was not abundant in central parts of lake Donghu, which were periodically hypoxic during summer and early autumn. The lake Donghu benthic community is typical for eutrophic lake and is dominated by chironomids and oligochaetes (Jonasson, 1984;Devine and Vanni, 2002). In general, we find distribution patterns similar to those reported by previous studies (Chen and Wu, 1990;Wang, 1996;Gong et al, 2000).…”

“…Interspecies differences in SRP excretion rates were found also in other studies: between the rotifera Euchlanis dilatata (18-19 ºC) and other rotifers (Gulati et al, 1989) as well as between Dreissena polymorpha and D. bugensis (Conroy et al, 2005). At the same time, Devine and Vanni (2002) showed that differences in SRP excretion rate between taxa are not significant and this rate depend mostly on temperature and biomass. Also, it probably might be a result of difference in food resources accumulated in littoral and deepwater sites of the lake, but this question needs future research.…”

“…At the same time, estimated in littoral site of Guozhenghu, maximum SRP excretion rate from benthos (173 µmol P·m -2 ·d -1 ) is a major portion (62%) of the maximum total phosphorus release in this lake. Other studies also show that contribution of SRP excretion by benthic animals to the total phosphorus release is very important and is usually varying between 4 and 17% (Andersson et al, 1988;Devine and Vanni, 2002;Postolache et al, 2006). Furthermore, in dry years with low phosphorus input from watershed phosphorus excretion mediated by animals can reach maximum 90% of the total phosphorus release (Devine and Vanni, 2002).…”

“…Several works confirm that specific benthic community SRP excretion rates increasing with temperature. These relationships cause the summer and winter (seasonal) differences in phosphorus fluxes as in the case of zooplankton (Oude and Gulati, 1988) and benthic communities (Devine and Vanni, 2002;Postolache et al, 2006). These variations in SRP excretion rates are not only relate to characteristics of individual species/taxa but also reflect the character of environments and primarily trophic conditions in each case study.…”

Effect of habitat heterogeneity in the composition and distribution of Chironomidae (Diptera) assemblage in different microhabitats of preserved streams in the Brazilian Atlantic Forest

“…Benthic invertebrates are essential to the transformation of organic matter and nutrient cycling in aquatic environments (Graça, 2001;Devine and Vanni, 2002). The community represents an important component for the understanding of both structure and functioning of aquatic communities, as well as the ecological processes related to hydrological variations (Vannote et al, 1980).…”