Ian P. Morrissey

Riparian seed banks: structure, process and implications for riparian management

After a brief description of the evolution of seed bank research, this review highlights the importance of the seed bank in understanding the character and dynamics of river margins. Through a discussion of published research on wetlands in general, the lack of research focused on riparian systems is highlighted. This is followed by an evaluation of current knowledge concerning the nature and dynamics of riparian seed banks and the factors that control the erosion, transport and deposition of riparian seeds. The paper concludes by (i) indicating the complexity of the interactions that control the riparian seed bank and that require understanding if the consequences of alterations in river flow regime and riparian management are to be fully understood and (ii) identifying some major research gaps relating to interactions between fluvial processes and riparian seed banks.

Riparian seed banks along the lower River Dove, UK: their structure and ecological implications

This paper investigates associations between the viable seed bank, sediment properties and elevation on three eroding river banks along the lower reaches of the River Dove, Derbyshire, UK. Using both descriptive statistics and detrended correspondence analysis, major contrasts are found in the abundance and floristic composition of the viable seed bank between the bank top, bank face and bank toe and between the three study sites. Canonical correspondence analysis identifies associations between the floristic composition of the seed bank and the percent organic matter, percent clay, percent sand and median particle size of the soil matrix that contains the seeds. The patterns revealed by the above analyses indicate (i) an increasing influence of fluvial processes (hydrochory) on the species composition of the seed bank with decreasing elevation; (ii) a low abundance of viable seeds on unvegetated eroding bank sections, suggesting limited long-term storage of viable seeds within floodplain sediments; and (iii) a very substantial seed bank where old channel sections provide a local depositional environment. The implications of these observations for understanding the role of fluvial processes in riparian seed bank dynamics and their implications for riparian management are discussed.

Longitudinal variations in exposed riverine sediments: a context for the ecology of the Fiume Tagliamento, Italy

1. A key component of physical habitat along braided river systems is the exposed riverine sediment within the active zone. The relatively unmanaged, gravel-bed Fiume Tagliamento, Italy, provides the focus for exploring two ecologically important properties of exposed riverine sediments: their within-patch and between-patch variability in calibre. 2. To characterize between-patch variation in exposed riverine sediments, replicate (within-patch) samples were obtained from three geomorphologically distinct locations along 130 km of the river: bar heads along the margin of the low-flow channel, the heads of major bars across the exposed surface of the active zone, and floodplain surfaces. A photographic technique enabled rapid and consistent field sampling of the coarse sediments at bar heads along the low-flow channel margin and on major bars across the dry bed. 3. A downstream decrease in particle size and an increase in within-patch heterogeneity in sediment size were observed within bar head sediments along the margin of the low-flow channel. Comparisons between major bar and low-flow channel samples revealed greatest within-patch variability in individual sediment size indices (D50, A- and B-axes of the larger particles) at headwater sites, greatest between-patch variability in the three measured indices in the central reaches, and lowest between-patch variability at downstream sites. However, there was a distinct increase in the overall heterogeneity in particle size, which was sustained across all patches, in a downstream direction. 4. There was a clear downstream decrease in the size of floodplain sediments in the headwaters, but thereafter there was no distinct downstream trend in any of the calculated particle size indices. 5. The geomorphological controls on the observed patterns and the potential ecological significance of the patterns, particularly for plant establishment, are discussed in relation to the relative relief of the active zone, and the highly variable hydrological and climatic regime along the river.

Morphological and ecological change on a meander bend: the role of hydrological processes and the application of GIS

Environmental change induced by hydrological processes can often be quite small. This paper illustrates subtle changes in river planform on a single meander bend of the lower River Dee, Wales, and the significance of those changes for the ecology of the present riparian zone. Geographical information systems (GIS) are shown to provide an excellent framework for integrating historical and contemporary information from different sources, and for quantifying possible transcription errors so that true environmental associations and relatively small changes, in the context of the spatial scales of the sources, can be identified with confidence. As a result, functional units within the riparian zone of a regulated river can be defined and mapped.

DYNAMICS OF WATER MOVEMENT AND TRENDS IN DISSOLVED CARBON IN A HEADWATER WETLAND IN A PERMEABLE CATCHMENT

We examined trends in the movement and source of water in a headwater wetland in North Shropshire, UK. Six piezometer nests along two transects were monitored over an 18 month period, and flownets were derived to estimate the rate and direction of water movement through the wetland and the interaction between precipitation and groundwater discharge. Individual water sources are identified using stable isotopes and seasonal differences in the composition of wetland soil-water are described. Variations in dissolved inorganic and organic carbon (DIC and DOC) were measured in water samples collected from discrete points in the wetland and the adjacent river and were interpreted using the hydrological data. The results suggest that end-members for DOC and DIC can be identified across the range of sampling sites: a groundwater spring (GS) had the lowest DOC and high DIC (DOC = 5.6 ± 4.5 mg/l; DIC = 36.7 ± 4.6 mg/l); a shallow well (WS) had the highest DOC and DIC (DOC = 32.5 ± 18.7 mg/l; DIC = 61.9 ± 18.9 mg/l); while surface-water (WSW) had the lowest DIC (20.6 ± 12.1 mg/l). Water fluxes between the wetland and river are estimated using the Dupuit-Forcheimer approximation to highlight the degree to which some headwater wetlands may act as a carbon source to ecosystems downstream. These wetlands are potentially a significant pool of C but are particularly sensitive to future changes in groundwater levels.