The relationship between land use and physicochemistry, food resources and macroinvertebrate communities in tributaries of the Taieri River, New Zealand: a hierarchically scaled approach

Abstract

1. The relationship between land use and stream conditions was investigated, including physicochemistry, the availability of primary food resources and species richness, species composition and trophic structure of stream macroinvertebrate communities. The survey involved eight subcatchments of the Taieri River (New Zealand) encompassing reasonably homogeneous examples of four major land uses: native forest, native tussock grassland, plantations of introduced pine and agricultural pasture. 2. Each land use was represented by two subcatchments, each subcatchment by two to four tributaries, and each tributary by two to three sampling sites. These three sampling scales each represent typical designs for stream community studies. By recording responses at all scales, it can be determined explicitly whether the scale of sampling influences interpretation of community structure. 3. Elevation, riffle length, proportion of large substrata in the bed, total phosphorus and alkalinity were significantly related to land use, as were canopy cover and the relative abundance of leaves and wood in the streams. Principal components analysis of invertebrate density data identified nine orthogonal community types, the distributions of two of which were significantly related to land use. The role played by browsers and shredders in the stream community depended on land use. 4. Primary analysis was at the level of the tributary. When it focused on sites within tributaries, more variables were related to land use and at a higher level of significance. This was largely a result of enhanced statistical power due to increased replication. When whole subcatchments were the focus of attention, statistical power was so low, even with six to eleven subsamples to generate overall means, that few significant patterns could be identified. However, the community patterns that were revealed were similar whatever the scale of sampling.

Macroinvertebrate functional organization and water quality in a large arid river from Patagonia (Argentina)

“…The fact that the collector filterers (Hydropsychidae, Simulidae) were abundant at upper basin tributaries (T1 and T2) responded to a significant habitat complexity that possibly enhanced organic matter retentions and availability of suspended organic matter. Similar observations have been reported by Bis et al (2000) and Townsend et al (1997) in native forest streams. The absence of collector-filterers right below the impoundment could be related with the discontinuities in seston supply below large impounded rivers (Troesltrup & Hergenrader 1990).…”

Primary consumers and resources: Annual variation in two contrasting reaches of a Patagonian mountain stream

“…We would expect significantly higher leaf detritus in forested than in open, downstream reaches (Stout et al, 1993;Townsend et al, 1997;Benstead et al, 2003). However, downstream movement of detritus is a major phenomenon in lotic systems.…”

“…Indeed, the "river continuum concept" (RCC) postulates that macroinvertebrates feeding on leaf litter (detritivorous shredders) will decrease from low order, forested streams to higher order streams with open canopy while grazers (mostly scrapers) are predicted to increase in biomass in the downstream open reaches (Vannote et al, 1980;Rosi-Marshall and Wallace, 2002). These changes have also been observed in streams affected by deforestation or fire (Townsend et al, 1997;Minshall, 2003;Benstead and Pringle, 2004).…”

Effects of catchment disturbance on stream invertebrates: comparison of different habitats (vegetation, benthic and interstitial) using bio-ecological groups.

“…Mean richness (± SE) calculated with the 4 replicate samples, streams noted with the same letter are not significantly different (ANOVA test). (11) communities with changes in land-cover (Townsend et al 1997) were linked to the accumulation of fine sediment and organic matter resulting from soil erosion (Culp et al 1983, Rempel et al 2000, the stimulation of micro and macrophyte growth (Madsen & Adams 1989), with increase in phytophilous organisms (Jenkins et al 1984, Rutt et al 1989). In our study, the changes in aquatic fauna were more pronounced with increasing agriculture intensity, but with an unexpected pattern.…”

“…A third explanation may be the resistance of the dominant taxa to disturbances: several species of Nematoda and Oligochaeta are known to resist to decrease in water quality and to fine sediment increase (e.g. Townsend et al 1997). …”