A nine-year study of the macroinvertebrate fauna of a chalk stream

Abstract

Abstract:The macroinvertebrate fauna of a 50 m site on a partially shaded perennial section of the River Lambourn in Berkshire was studied intensively between 1971 and 1979. This period included a minor drought in 1973 and a major drought in 1976.A quantitative sampling programme for macroinvertebrates was undertaken on each of ®ve distinct biotopes (Berula, Callitriche, Ranunculus, gravel and silt). Each one was sampled in March, June, September and December of 1971 and thereafter in June and December from 1972 to 1979. Five replicate sampling units from each biotope were processed separately prior to determination of density estimates, except in 1972 and 1973, when time constraints necessitated bulking and subsampling.Family richness per sampling unit and per sample was higher in December than June, and higher on the three macrophytes than on gravel and silt. Nevertheless, over nine years, a high proportion of the 59 families recorded on the site were collected on each biotope.During the extreme drought of 1976, there was no evidence of loss of family richness on the site, but some biotopes supported unusually high densities of macroinvertebrates from a limited number of families. By combining information on the density of invertebrates per biotope and the area of each biotope, the weighted mean density of invertebrates on the site was calculated for each sampling occasion.Seasonal and between-year changes in the densities of numerically important families were observed and a variety of responses to discharge regime were noted. Overall, the macroinvertebrate fauna appeared to be capable of rapid recovery after an extreme drought event on this unpolluted perennial site.

Macroinvertebrate community dynamics in a temperate European Atlantic river. Do they conform to general ecological theory?

“…Therefore, we believe that the seasonal dynamics of macroinvertebrate number of taxa in the Pas river basin is primarily driven by the temporal segregation of taxa in relation Macroinvertebrate abundance increased downstream and was almost four times higher in the low flow period (summer) compared to the high one (winter), what is consistent with our second prediction. Similar spatial and temporal patterns have been reported for macroinvertebrate communities of other Atlantic rivers from northern Spain (Riaño et al, 1993;Basaguren et al, 1996;Otermin et al, 2002) and England (Wright & Symes, 1999). Both Riaño et al (1993) and Basaguren et al (1996) suggested that macroinvertebrate abundance is lower in headwaters due to higher hydraulic stress, which can reduce macroinvertebrate food resources such as periphytic biomass (Clausen & Biggs, 1997;Izaguirre & Elosegui, 2005) and the concentration of organic matter (Giller & Malmqvist, 1997).…”

“…Many studies of temperate Atlantic rivers have focused on the effects of unpredictable hydrological disturbances on macroinvertebrate communities (Riaño et al, 1993;Basaguren et al, 1996;Feminella, 1996), but few have reported macroinvertebrate community changes in relation to hydrological predictability during an average hydrological year. However, Wright & Symes (1999), after 10 years of study in the Lambourn River (UK), described higher macroinvertebrate density during the average summer as a consequence of an increase in lentic taxa (e.g. Chironomidae), which were replaced by more reophilic macroinvertebrate families (e.g.…”

Persistence of Hydrometeorological Droughts in the United Kingdom: A Regional Analysis of Multi-Season Rainfall and River Flow Anomalies

“…Another study of the macroinvertebrate fauna of the River Lambourn during the extreme drought of 1976 found no evidence of loss of family richness but unusually high densities for some families, with rapid recovery at an unpolluted perennial site following drought termination (Wright and Symes, 1999). However, the recovery of invertebrate communities from much longer droughts is poorly understood and confounded by anthropogenic modifications to habitat and river flow (Bond et al, 2008).…”

Organic matter availability during pre- and post-drought periods in a Mediterranean stream

“…As the dry season progresses and water flow is even more reduced, habitat conditions become harsher (Gasith & Resh, 1999), transport of OM (detritus, leaves and plant material) and fine sediments declines and high quantities of OM are stored in pools (Cuffney & Wallace, 1989;Boulton & Lake, 1992;Wright & Symes, 1999). In addition, conductivity and water temperature rise, and low oxygen levels lead to facultative aerobic and anaerobic respiration.…”