Abstract
AbstractSedimentation is a pervasive environmental pressure affecting rivers globally. Headwaters draining catchments rich in organic soils (i.e., peat) are particularly vulnerable to enhanced sedimentation caused by land management and environmental change, yet many of the ecological consequences of peat deposition are poorly understood. We conducted a before‐after‐control‐impact experiment in two rivers draining blanket peatland in Northern England to test the effect of sediment inputs on water quality, macroinvertebrate drift, macroinvertebrate community structure, and ecosystem metabolism. Sediment addition increased concentrations of dissolved organic carbon, total oxidised nitrogen and suspended sediment concentration in rivers, and intensified the total drift of macroinvertebrates particularly at night. By contrast, the abundance and richness of benthic macroinvertebrates were unaffected, except for declines in Coleoptera abundance in one river. The gross primary production of both rivers was strongly suppressed as the benthos was smothered by sediment. Community respiration also declined, albeit by different extents in the two rivers. Our experiment revealed that short‐term pulses of organic sediment in rivers can have broad effects on water quality and biota, from influences on the dispersal of individual organisms to the modification of ecosystem processes. Organic sediments therefore warrant further examination, to include longer observation periods and more sites. It is particularly important to clarify the extent to which impacts extend from peatland streams into larger rivers downstream. Such studies are necessary to inform global management efforts to restore the integrity of river ecosystems under a range of water and biodiversity policy mechanisms.
Highlights
Sedimentation is a major cause of ecological degradation in freshwater ecosystems, with artificially enhanced delivery and retention of fine sediments in rivers and lakes a significant global problem (Dudgeon et al, 2006; Larsen & Ormerod, 2010; Piggott, Townsend, & Matthaei, 2015; Wood & Armitage, 1997)
This paper reports the results of a manipulative experiment to quantify the short‐term impacts of organic sediment inputs on the water quality and ecology of two peatland rivers in Northern England, scaling from populations and communities to ecosystem processes
Short‐term sediment addition experiments have provided novel insights into the implications of sediment influx for headwater river ecosystems, showing notable changes to water quality, which may be different to inorganic sediments and across different levels of ecological organisations
Summary
Sedimentation is a major cause of ecological degradation in freshwater ecosystems, with artificially enhanced delivery and retention of fine sediments in rivers and lakes a significant global problem (Dudgeon et al, 2006; Larsen & Ormerod, 2010; Piggott, Townsend, & Matthaei, 2015; Wood & Armitage, 1997). Mortality and local extinction of sensitive species (Kemp et al, 2011; Wood & Armitage, 1997) can occur, with the remaining sediment‐tolerant biota becoming unusually dominant (Larsen & Ormerod, 2010) Such marked shifts in community structure can impair key ecosystem processes for a variety of groups, including benthic algae and macrophytes (Izagirre, Serra, Guasch, & Elosegi, 2009; Jones, Duerdoth, Collins, Naden, & Sear, 2014), macroinvertebrates (Culp, Wrona, & Davies, 1986; Extence et al, 2013; Larsen, Pace, & Ormerod, 2010), and fish, especially salmonids (e.g., Greig, Sear, & Carling, 2005). We hypothesised that (H4) sediment smothering of algal biofilms would suppress GPP but stimulate CR via enhanced consumption of available particulate and dissolved organic matter by heterotrophs (Izagirre, Bermejo, Pozo, & Elosegi, 2007; Roberts, Mulholland, & Hill, 2007)
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