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Circumneutral Streams (circumneutral + stream)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Effects of acidification on the breeding ecology of a stream-dependent songbird, the Louisiana waterthrush (Seiurus motacilla)

FRESHWATER BIOLOGY, Issue 11 2008
ROBERT S. MULVIHILL
Summary 1.,We compared breeding ecology of the Louisiana waterthrush (Seiurus motacilla) on acidified and circumneutral streams in the Appalachian Highlands of Southwestern Pennsylvania from 1996 to 2005. 2.,Headwater streams impacted by acid mine drainage and/or acidic precipitation showed reduced pH (range 4.5,5.5) compared to four circumneutral streams (pH c. 7). Acid-sensitive taxa, including most mayflies (Ephemeroptera), were almost completely absent from acidified streams, whereas several acid-tolerant taxa, especially stonefly (Plecoptera) genera Leuctra and Amphinemura, were abundant. 3.,Louisiana waterthrush breeding density (c. 1 territory km,1) was significantly reduced on acidified streams compared to circumneutral streams (>2 territories km,1). Territories on acidified streams were almost twice as long as on circumneutral streams. Territories usually were contiguous on circumneutral streams, but they were often disjunct on acidified streams. Breeding density declined on one acidified stream that we studied over a 10-year period. 4.,Clutch initiation was significantly delayed on acidified streams, on average by 9 days in comparison to circumneutral streams, and first-egg dates were inversely related to breeding density. Birds nesting along acidified streams laid smaller clutches, and nestlings had shorter age-adjusted wing lengths. Stream acidity had no effect on nest success or annual fecundity (fledglings/female). However, the number of young fledged km,1 was nearly twice as high on circumneutral streams as on acidified streams. 5.,Acidified streams were characterized by a younger, less site-faithful breeding population. Individuals were less likely to return multiple years to breed, allowing inexperienced breeders to settle on acidified streams. Pairing success was lower on acidified streams, and we observed four cases of waterthrushes emigrating from territories on acidified streams to nearby circumneutral streams in the following year. 6.,We conclude that acidified headwaters constitute lower quality habitat for breeding Louisiana waterthrush. However, breeding birds can apparently compensate for reduced prey resources to fledge young on acidified streams by increasing territory size, foraging in peripheral non-acidified areas, and by provisioning young with novel prey. [source]

Growth and population size of crayfish in headwater streams: individual- and higher-level consequences of acidification

FRESHWATER BIOLOGY, Issue 7 2004
Steven M. Seiler
Summary 1. Environmental stress may have indirect positive effects on population size through modification of food-web interactions, despite having negative effects on individuals. Here we evaluate the individual- and population-level effects of acidification on crayfish (Cambarus bartonii) in headwater streams of the Allegheny Plateau (PA, U.S.A.) with field experiments and survey data. Median baseflow pH of 24 study reaches in nine streams varied from 4.4 to 7.4, with substantial variation found both among and within streams. 2. Two bioassays were conducted to evaluate the relationship between stream pH and crayfish growth rates. Growth rates were always higher in circumneutral reaches than in acidic reaches. Crayfish originating in acidic water grew less when transplanted into neutral water than did crayfish originating in neutral water, providing some evidence for a cost of acclimation to acidity. 3. Stream surveys showed that fish were less abundant and crayfish more abundant in acidified streams than in circumneutral streams. Crayfish density was sixfold higher in reaches with the lowest pH relative to circumneutral reaches. Large crayfish made up a higher proportion of crayfish populations at sites with high fish biomass, consistent with the hypothesis that fish predation on small individuals may be limiting crayfish population size at these sites. 4. Although individual crayfish suffered lower growth in acidified streams, increased acidity appeared to cause an increase in crayfish population size and shifts in size structure, possibly by relieving predation pressure by fish. [source]

Climate change effects on upland stream macroinvertebrates over a 25-year period

GLOBAL CHANGE BIOLOGY, Issue 5 2007
ISABELLE DURANCE
Abstract Climate change effects on some ecosystems are still poorly known, particularly where they interact with other climatic phenomena or stressors. We used data spanning 25 years (1981,2005) from temperate headwaters at Llyn Brianne (UK) to test three hypotheses: (1) stream macroinvertebrates vary with winter climate; (2) ecological effects attributable to directional climate change and the North Atlantic Oscillation (NAO) are distinguishable and (3) climatic effects on macroinvertebrates depend on whether streams are impacted by acidification. Positive (i.e. warmer, wetter) NAO phases were accompanied by reduced interannual stability (=similarity) in macroinvertebrate assemblage in all streams, but associated variations in composition occurred only in acid moorland. The NAO and directional climate change together explained 70% of interannual variation in temperature, but forest and moorland streams warmed respectively by 1.4 and 1.7°C (P<0.001) between 1981 and 2005 after accounting for NAO effects. Significant responses among macroinvertebrates were confined to circumneutral streams, where future thermal projections (+1, +2, +3°C) suggested considerable change. Spring macroinvertebrate abundance might decline by 21% for every 1°C rise. Although many core species could persist if temperature gain reached 3°C, 4,10 mostly scarce taxa (5,12% of the species pool) would risk local extinction. Temperature increase in Wales approaches this magnitude by the 2050s under the Hadley HadCM3 scenarios. These results support all three hypotheses and illustrate how headwater stream ecosystems are sensitive to climate change. Altered composition and abundance could affect conservation and ecological function, with the NAO compounding climate change effects during positive phases. We suggest that acidification, in impacted streams, overrides climatic effects on macroinvertebrates by simplifying assemblages and reducing richness. Climatic processes might, nevertheless, exacerbate acidification or offset biological recovery. [source]