The riparian zone occupies the critical interface between land and watercourses where processes have great potential to influence stream and river biogeochemical and ecological conditions and is a key management location. Riparian influences on water quality may arise from:
We make a distinction between the riparian zone and a buffer zone. The former implies a zone with a gradient of hydrological, habitat and geomorphic change from land to channel, the latter implies a management zone designed to separate potentially negative pressures of land activities from the aquatic ecosystem. There has been considerable debate over minimum riparian buffer widths for protection of stream ecosystems (e.g. Sweeney & Newbold, 2014). Hansen et al. (2015) found that studies collectively supported needs for variable buffer widths to protect watercourses depending on circumstances but the available body of riparian literature insufficiently or inconsistently reported the landscape contexts necessary to explain inter- and intra- study variability in outcomes. Hence, riparian structure and functions, both current and potential and informed strongly by landscape setting, are required to be considered alongside the environmental objectives (such as maintaining, or improving water quality and other multiple benefits).
Figure 1. Schematic of how assessment of presures, riparian indicators of function and relationships with water quality parameters contributes to the two aims of the current review.
Figure 1 shows twofold aims that guide this current review. The first concerns the spatial targeting of understanding and management to maintain and restore riparian functions, to design and place effective riparian buffer zones. The second aim is to give catchment scientists improved methods for characterising important catchment riparian functions that relate to water quality to improve evidence on the connection between riparian condition and water quality to facilitate better management. The delineation of riparian zones is a key requirement of riparian management, forming a basis for the understanding the optimal zones to maintain or restore critical riparian functions. Yet delineation remains challenging and the literature suggests a variety of methods that have not been reviewed previously. This review examines:
There are numerous schemes for assessment of riparian functions and key functions themselves concentrated on by regulatory actions. An example of a full description of a long-time implemented assessment scheme is given by Swanson et al. (2017) for the riparian Proper Functioning Condition (PFC) assessment that is integrated with, and assessed against, water quality monitoring in Nevada, U.S. The PFC assessment is based on scoring indicators of vegetation, hydrology and geomorphology against potential natural condition with regard to provision of functions: dissipation of stream energy, capturing sediment, increasing water recharge, rooting and bank stability, maintaining channel characteristics. Such core functions are common to many riparian assessment studies. The structure of section 2 here expands on this grouping according to: hydrological connectivity, water quality, shading and temperature regulation, resource transfers and terrestrial habitat. We describe indicators of the functions prior to assessing how these functions and their data are currently integrated into riparian delineation in Section 3
The dominant process groups are briefly presented below and key studies are indicated in Table 1
This section is structured according to different methods of representing riparian processes spatially (Figure 2) considering simple fixed to more complex variable width methods.
Figure 2. Schematic of different riparian situations to illustrate the three main classes of riparian delineation considered here: fixed width, variable width by attributes and variable width by local context and required outcomes, together with eight submodels.
Fixed width approaches
Variable width criteria - Researchers have advocated variable width approaches accounting for site-specific conditions. A challenge is that many functions and processes have to be represented with different styles, availabilities and resolutions of data. If the data are available the clear benefit of such an approach is that it considers the extent of important ecological functions, whereas fixed width methods are seldom ecologically-based.
Considering local context in deriving functions necessary for resource protection - The width of riparian buffer zones should depend on the ecological functions that need to be protected for a given local ecosystem circumstance and the multiple pressures acting on it. This implies (i) an ability to define the risk of the pressure from the adjacent land and (ii) to determine key interaction factors of buffer functions (e.g. hydrological connectivity for pollutant transport pathways, roughness for erosion trapping efficiency, soil organic carbon for in-situ organic contaminant degradation). Different approaches in the literature include:
Working backwards from a required level of protection of water resources (e.g. aquatic ecology, drinking water protection; ie delineation model 3viii) are considerably less reported are since these require holistic knowledge of the pressure-state-response of the ecosystems.
It is key to represent riparian hydrological interactions of:
The approach of Riparian Hydrological Types reported by Dahl et al. (2007) seems valid for assessing vulnerability of riparian and stream ecology to aspects of water table stability, baseflow generation, temperature and nutrient supply via water exchanges. Research tools to aid this were not commonly reported, although one was the open GIS-based tool ‘FluvialCorridor’ (Roux et al., 2015) and core datasets for such tools are likely to be country-specific.
Stutter, M., Baggaley, N., & Wang, C. 2020. The utility of spatial data to delineate river riparian functions and management zones: a review [3]. Science of The Total Environment, 143982.
Links:
[1] https://www.hutton.ac.uk/sites/default/files/images/Fig1_delcritzones_crp_resize.png
[2] https://www.hutton.ac.uk/sites/default/files/images/Fig2_RipSit_res_flat.jpg
[3] https://www.sciencedirect.com/science/article/abs/pii/S0048969720375136
[4] https://www.hutton.ac.uk/staff/marc-stutter
[5] https://www.hutton.ac.uk/staff/miriam-glendell
[6] https://www.hutton.ac.uk/staff/rachel-helliwell
[7] https://www.hutton.ac.uk/staff/adekunle-ibiyemi
[8] https://www.hutton.ac.uk/staff/chen-wang
[9] https://www.hutton.ac.uk/staff/margaret-mckeen
[10] https://www.hutton.ac.uk/research/projects/rd-121-water-and-its-ecosystem-functions
[11] https://www.hutton.ac.uk/research/srp2016-21/wp122-impacts-change-water
[12] https://www.hutton.ac.uk/research/srp2016-21/wp123-water-environment-resilience-and-adaptation-change
[13] https://www.hutton.ac.uk/research/srp2016-21/wp124-effectiveness-water-management
[14] https://www.hutton.ac.uk/research/projects/catchment-typologies-risk-and-resilience