Stream biodiversity: The ghost of land use past

Abstract

The inf luence of past land use on the presentday diversity of stream invertebrates and fish was investigated by comparing watersheds with different land-use history. Whole watershed land use in the 1950s was the best predictor of present-day diversity, whereas riparian land use and watershed land use in the 1990s were comparatively poor indicators. Our findings indicate that past land-use activity, particularly agriculture, may result in long-term modifications to and reductions in aquatic diversity, regardless of reforestation of riparian zones. Preservation of habitat fragments may not be sufficient to maintain natural diversity in streams, and maintenance of such biodiversity may require conservation of much or all of the watershed.Conservation of species diversity at local, regional, and continental scales has received increasing attention as human disturbance and modification of ecosystems increase. Our understanding of the magnitude of species decline is clearest for vertebrates in terrestrial, marine, and lake ecosystems (1-4). In contrast, empirical evidence of extirpations and extinctions of invertebrate species in lotic (running water) ecosystems is comparatively sparse (1-9). Worldwide, many rivers and streams have been profoundly modified by urban and agricultural development, impoundment, channelization, resource-extraction projects, and pollution. In many regions, such as the southern Appalachian Mountains, reforestation of previously cleared watersheds is occurring as agriculture becomes less important to the local economy (10, 11). This process of reforestation allows us to ask: to what extent are the effects of human disturbance reversible, and how long does recovery take? Although recovery and restoration of the physical habitat is often possible, the degree to which biological communities can recover from long-term disturbance is still relatively unknown.Stream ecologists have long recognized the strong dependence of streams on the surrounding terrestrial environment (12-15). The riparian zone bordering streams serves as a buffer between the stream and the surrounding watershed and is also the primary source of organic matter for many small streams in forested biomes (12)(13)(14)(15). Conditions in the riparian zone, therefore, strongly influence stream hydrology, substrate characteristics, temperature regimes, and water chemistry, which in turn affect all trophic levels. Considerable emphasis has been placed on protection or revegetation of riparian zones as a tactic for preserving aquatic ecosystems (16,17). The presence of natural vegetation in riparian zones has been shown to improve stream hydrology, water quality, and reduce sedimentation in disturbed watersheds (18)(19)(20). However, by emphasizing restoration of riparian zones, land managers assume that stream conditions across the whole catchment can be mitigated by attention only to land adjacent to the stream. This assumption is not supported by recent studies (21, 22).The overall objective of the present study was to inves...

Quantifying the effect of catchment land use and water nutrient concentrations on freshwater river and stream biodiversity

“…Conflicting results may in some cases be explained by the difficulties of separating present-day LAND USE AND NUTRIENT EFFECTS ON FRESHWATER BIODIVERSITY from historical influences (Allan, 2004). As Harding et al (1998) clearly showed, the effect of past land use changes can have a major influence on the present-day fish species in rivers and streams. It was not possible to take historical changes into account in this study, as it was dependent on the information given in the articles used.…”

“…Upper and lower confidence levels (95%) are depicted in dashed lines. Data are based on studies by Harding et al, 1998;Sponseller et al, 2001;Collier and Quinn, 2003;Harding, 2003;and Bruns, 2005. This study shows that altered catchment land use can have a major effect on freshwater taxon diversity and that the rate of species loss is serious; from the literature reviewed, every 10% of lost natural catchment land cover led to an average loss of almost 6% ( AE 0.83) of the native freshwater fish and macroinvertebrate species. Quantifying relationships makes it possible to emphasize to policy makers the consequences of continued habitat alteration and eutrophication, and to visualize the costs of these actions in terms of taxon diversity loss.…”

“…Upper and lower confidence levels (95%) are depicted in dashed lines. Data are based on studies by Roth et al, 1996;Harding et al, 1998;Marchetti and Moyle, 2001;Joy and Death, 2004;and Schweizer and Matlack, 2005. Figure 4.…”

“…Upper and lower confidence levels (95%) are depicted in dashed lines. Data are based on studies by Harding et al, 1998;Euliss and Mushet, 1999;Hall et al, 2001;Sponseller et al, 2001;Bojsen and Jacobsen, 2003;Collier and Quinn, 2003;Harding, 2003;and Bruns, 2005. Linear regression between the percentage of non-natural cover in the catchment and EPT taxon diversity in streams.…”

Large‐scale relationships between basin and riparian land cover and the ecological status of European rivers

“…Moreover, physical alterations caused by agriculture can generate biological impacts over decades (Harding et al, 1998). Other authors have found less negative effects (Meador & Goldstein, 2003), or even positive relationships between agricultural land cover and invertebrate diversity (Moore & Palmer, 2005).…”