The importance of excretion by Chironomus larvae on the internal loads of nitrogen and phosphorus in a small eutrophic urban reservoir

Abstract

Measurements of ammonium and phosphate excretion by the Chironomus larvae were conducted in order to evaluate the importance of these chironomids for the internal loads of a small eutrophic urban reservoir. Ammonium and phosphate excretion rates by Chironomus larvae of small size (6-10 mm total length) were significantly higher than those of the Chironomids having medium (9-11 mm) and large (11-16 mm) sizes. A dependence in relation to temperature was recorded for the ammonium and phosphate excretions that was significantly higher at 25 °C than at 20 and 15°C. Through a linear relation between biomass (dry weight) and total length and, between excretion and biomass and, data on chironomids densities, after an intense sampling in 33 sites distributed all along the reservoir bottom, the mean phosphate and ammonium excretion rates corresponded to 2,014 5,134 g.m ) and the mean excretion rates, the contribution of benthic chironomids to the internal loads would be 181 KgP and 147 KgN. for the sampling months (October-November 1998). These values showed that the internal loads by excretion from Chironomus larvae correspond to approximately 33% of the external loads of phosphorus in the lake and, in the case of nitrogen, to only 5%.Keywords: excretion, Chironomus, internal load, reservoir, nutrients. Excreção por quironomídeos em reservatório urbano ResumoMedidas de excreção de amônia e fosfato por larvas de Chironomus foram executadas com a finalidade de avaliar a importância desses quironomídeos nas cargas internas de um pequeno reservatório urbano eutrófico. Taxas de excreção de amônia e fosfato significativamente mais elevadas foram encontradas nas larvas de Chironomus de pequeno (6-10 mm) tamanho, em relação às de tamanho médio (9-11 mm) e grande (11-16 mm). Uma dependência em relação à temperatura foi registrada para a excreção de amônia e fosfato, significativamente mais alta a 25 °C do que a 20 e 15°C. Depois da obtenção das relações lineares entre biomassa (peso seco) e comprimento total e excreção com biomassa e dos dados de densidade de quironomídeos, após amostragem em 33 pontos distribuídos por todo o reservatório, foi possível estimar uma taxa média de excreção de fosfato de 2014 5134 g.m 2 ) e as taxas médias de excreção, a contribuição dos quironomídeos bênticos para as cargas internas seria de 181 KgP e 147 KgN, para o mês da amostragem (outubro-novembro de 1998). Esses valores mostraram que as cargas internas por excreção pelas larvas de Chironomus correspondem aproximadamente a 33% das cargas externas de fósforo para o lago e, somente 5% no caso de nitrogênio.

Benthic macroinvertebrates of a tropical lake: Lake Caçó, MA, Brazil

“…However, on account of their importance in ecological processes, studies on these communities in Brazilian waters have noticeably gained importance (Nessimian, 2005;Davanso and Henry, 2007;Strixino and Trivinho-Strixino 1998;Callisto et al, 1998;Moreno and Callisto, 2006;Gonçalves et al, 2007;Fidelis et al, 2008;Henry and Santos, 2008).…”

Controlling factors of benthic macroinvertebrates distribution in a small tropical pond, lateral to the Paranapanema River (São Paulo, Brazil)

“…Comparative studies of small water bodies have been used to examine the relationships between environmental factors and the structure of aquatic communities (Heino, 2000). Benthic macroinvertebrates present great importance in some ecological processes, such as energy fluxes and nutrient cycling (Leal et al, 2003;Henry and Santos, 2008). Bioturbation of sediment surface and fragmentation of leaves from riparian vegetation are some of the processes of nutrient release to water carried out by benthic organisms (Caliman et al, 2007;Callisto et al, 2009).…”

Effect of the Environmental Factors on the Caloric Content of Benthic and Phytophilous Invertebrates in Neotropical Reservoirs in the Paraná State, Brazil

“…Therefore, additional studies on invertebrates will contribute to the better understanding of the energy flow in neotropical ecosystems, as aquatic invertebrates play an important role in the trophic dynamics of freshwater ecosystems, mainly through their function of recycling nutrients and detritus (HENRY and SANTOS, 2008). Knowledge about the energy content that these organisms provide to the food chain (CYR and DOWING, 1988; VAN DEN BRINK et al, 1994) is essential for an integrated understanding of the diet of invertebrate and vertebrate consumers.…”