Small Water Bodies in Great Britain and Ireland: Ecosystem function, human-generated degradation, and options for restorative action

Abstract

Small, 1st and 2nd-order, headwater streams and ponds play essential roles in providing natural flood control, trapping sediments and contaminants, retaining nutrients, and maintaining biological diversity, which extend into downstream reaches, lakes and estuaries. However, the large geographic extent and high connectivity of these small water bodies with the surrounding terrestrial ecosystem makes them particularly vulnerable to growing land-use pressures and environmental change. The greatest pressure on the physical processes in these waters has been their extension and modification for agricultural and forestry drainage, resulting in highly modified discharge and temperature regimes that have implications for flood and drought control further downstream. The extensive length of the small stream network exposes rivers to a wide range of inputs, including nutrients, pesticides, heavy metals, sediment and emerging contaminants. Small water bodies have also been affected by invasions of non-native species, which along with the physical and chemical pressures, have affected most groups of organisms with consequent implications for the wider biodiversity within the catchment. Reducing the impacts and restoring the natural ecosystem function of these water bodies requires a three-tiered approach based on: restoration of channel hydromorphological dynamics; restoration and management of the riparian zone; and management of activities in the wider catchment that have both point-source and diffuse impacts. Such activities are expensive and so emphasis must be placed on integrated programmes that provide multiple benefits. Practical options need to be promoted through legislative regulation, financial incentives, markets for resource services and voluntary codes and actions.

Keywords: Anthropogenic pressures; Ecosystem services; Headwaters; Ponds; Remediation; Streams.

Graphical abstract

Fig. 1

Mean and 95% Cl for 483 semi-natural River Habitat Survey (RHS) sites across the UK. Small steams (Strahler (1957) stream order 1 and 2), are characterised by, a) the steepest slopes (%), b) relatively few sediment storage features (bars) per unit length of channel (no/500 m), c) smallest bankfull channel widths (metres) and, d) highest substratum diversity within the river network (Shannon diversity index). Original Data from the Environment Agency, RHS database.

Fig. 2

Hourly precipitation (a), and discharge (b) in the River Dove, UK at Hollinsclough (8 km² headwater catchment) and Izaak Walton (≈30 km from source, draining 83 km² catchment) on 5–6 July 2012, illustrates rapid hydrological change in a headwater stream following an intense rain storm relative to the delayed and protracted response lower in the catchment.

Fig. 3

Channel modifications based on River Habitat Survey (RHS) data. Headwater streams (Strahler (1957) orders 1 and 2) have higher proportions of channel modifications: a) channel planform modifications through realignment; b) cross-section modification through dredging; c) major in-channel structures (bars are 95% CI for the mean).

Fig. 4

a) A highly simplified food web for a small stream showing the main feeding links (solid arrows) and non-feeding inputs (dashed arrows), and b) a real food web from a small, fishless stream without plants or terrestrial links (each numbered node represents a different food item/species which, with the exception of basal resources (unfilled circles), are all invertebrates: full details in Fig. 9 Schmid-Araya et al., 2002).

Fig. 5

Graphical representation of the three-tiered approach to reversing the decline of SWBs from a) degraded, to b) a state of improved resilience following restorative action.