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Sedimentation 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.

Land use and climate change are driving widespread modifications to the biodiverse and functionally unique headwaters of rivers. In temperate and boreal regions, many headwaters drain peatlands where land management and climate change can cause significant soil erosion and peat deposition in rivers. However, effects of peat deposition in river ecosystems remain poorly understood. We provide two lines of evidence—derived from sediment deposition gradients in experimental mesocosms (0–7.5 g/m2) and headwaters (0.82–9.67 g/m2)—for the adverse impact of peat deposition on invertebrate community biodiversity. We found a consistent negative effect of sediment deposition across both the experiment and survey; at the community level, decreases in density (1956 to 56 individuals per m2 in headwaters; mean 823 ± 129 (SE) to 288 ± 115 individuals per m2 in mesocosms) and richness (mean 12 ± 1 to 6 ± 2 taxa in mesocosms) were observed. Sedimentation increased beta diversity amongst experimental replicates and headwaters, reflecting increasing stochasticity amongst tolerant groups in sedimented habitats. With increasing sedimentation, the density of the most common species, Leuctra inermis, declined from 290 ± 60 to 70 ± 30 individuals/m2 on average in mesocosms and >800 individuals/m2 to 0 in the field survey. Traits analysis of mesocosm assemblages suggested biodiversity loss was driven by decreasing abundance of invertebrates with trait combinations sensitive to sedimentation (longer life cycles, active aquatic dispersal of larvae, fixed aquatic eggs, shredding feeding habit). Functional diversity metrics reinforced the idea of more stochastic community assembly under higher sedimentation rates. While mesocosm assemblages showed some compositional differences to surveyed headwaters, ecological responses were consistent across these spatial scales. Our results suggest short‐term, small‐scale stressor experiments can inform understanding of “real‐world” peatland river ecosystems. As climate change and land‐use change are expected to enhance peatland erosion, significant alterations to invertebrate biodiversity can be expected where these eroded soils are deposited in rivers.

ABSTRACT1. The restoration of riverine habitats that have been physically modified by man has gained momentum over the past two decades, driven by a number of objectives. Formalizing the planning and implementation of such activity, however, so that it demonstrably meets national and local environmental objectives without compromising essential societal needs such as flood risk management, has proved problematic.2. This paper addresses the operational realities of river restoration in the UK as experienced in England by the authors, and in doing so attempts to provide a vision for how strategic planning and implementation of restoration measures sensitive to these realities might be introduced. Specifically, the paper explores: the prevailing perspectives on river restoration, shaped by both legislative drivers for ecosystem and biodiversity protection and the multiple uses made of rivers, their floodplains and catchments; how decisions have tended to be made to date and how the government agencies for environmental protection and biodiversity conservation in England are planning to make decisions in the future; the key obstacles to putting in place scientifically and technically robust, large-scale, long-term, economically viable plans for river restoration; the potential for using rivers with special conservation designations for wildlife as a springboard for a strategic approach to river restoration more widely. 3. The issues hindering a strategic operational approach to river restoration in England are common to the rest of the UK and other developed countries grappling with the enormity of the river restoration challenge. To make real progress with river restoration, an operational decision-making framework is needed that promotes progressive and strategic action but at the same time gives everyone confidence that such action is realistic and worthwhile.

The interface between biodiversity and water management (i.e., conserving freshwater and wetland biodiversity) is a complex area in which to operate. The clash of decision‐making cultures arising from the separate evolution of biodiversity and water legislation and policy creates tensions that are not easily resolved. The complexity of the human pressures and stresses acting on freshwater and wetland ecosystems, and the multiplicity of specialisms and stakeholders required to address them, increase the challenges of working at this interface. There are therefore many people who need to have a common view of what we as a society are trying to achieve for freshwater ecosystems, and how each interested party best contributes to achieving this. There is a critical need for an ecological narrative that cuts through the legislative, operational, and technical complexity, providing a rationale for how biodiversity and water management can work together to achieve their respective objectives. Narratives provide an important function in circumstances where cultural mindsets drive decision making. They encourage decision making to be approached from a more holistic and strategic perspective without attempting to prescribe the outcome at a local level. The concept of natural ecosystem function provides a common language within which biodiversity and water objectives can be framed, and a coherent narrative has been developed in England with this concept at its heart. Allowing water to move through catchments as naturally as possible, in the most natural condition possible, lies at the heart of both biodiversity‐ and water‐based aspirations for freshwater and wetland ecosystems. WIREs Water 2017, 4:e1189. doi: 10.1002/wat2.1189 This article is categorized under: Water and Life > Conservation, Management, and Awareness Water and Life > Nature of Freshwater Ecosystems Water and Life > Stresses and Pressures on Ecosystems

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