Abstract
Wetlands are often promoted as a viable mitigation option to reduce nutrient export from both diffuse and point sources to adjacent surface
waters (lakes, rivers, streams). Much of the science used to promote them is, however, incomplete, relying on partial evidence on the
behaviour of some of the nutrient fractions (typically nitrate and phosphate, and occasionally ammonium) measured at a monthly frequency
at the outflow from the wetland, rather than holistic evidence demonstrating their dynamic function and how this varies in space and time, for
all nutrient forms. This leads to false assumptions about their ‘nutrient removal’ potential and a flawed evidence base for their wider use as
mitigation features in catchments.
Wetlands are complex, highly variable biogeochemical reactors in which a wide range of processes control the cycling and flux of nutrient
loading into, within and out of the wetland. Robust evidence on the net ‘storage’ or ‘removal’ of the entirety of the nutrient load entering the
wetland is essential to support effective policy and decision-making on whether they are the correct solution for eutrophication control.
Here, we:
1. Outline the processes controlling nutrient cycling in wetlands.
2. Offer a case study of a natural wetland, demonstrating its spatial (in terms of nutrient cycling) and temporal variability in cycling and
exporting accumulated nutrient loads to adjacent waters.
3. Present evidence on the bioavailability of dissolved and particulate nutrient fractions which, in many studies on wetlands as mitigation
features, are not measured at all.
4. Disprove the assumption (incorrect) in many mitigation efforts that only the inorganic nutrient fractions are bioavailable and cause
eutrophication impacts in freshwaters and demonstrate the need to take all nutrient fractions into account in policy and practice.
5. Provide a case study based on in-depth and holistic analysis of nutrient cycling and export in the Cromhall Constructed Wetland, owned
by Wessex Water and originally designed for the removal of phosphorus at a small rural water treatment centre.
Finally, we offer reflections on directions for future research which may assist in increasing nutrient removal potential in constructed wetlands
and summarise their longer-term limitations.
waters (lakes, rivers, streams). Much of the science used to promote them is, however, incomplete, relying on partial evidence on the
behaviour of some of the nutrient fractions (typically nitrate and phosphate, and occasionally ammonium) measured at a monthly frequency
at the outflow from the wetland, rather than holistic evidence demonstrating their dynamic function and how this varies in space and time, for
all nutrient forms. This leads to false assumptions about their ‘nutrient removal’ potential and a flawed evidence base for their wider use as
mitigation features in catchments.
Wetlands are complex, highly variable biogeochemical reactors in which a wide range of processes control the cycling and flux of nutrient
loading into, within and out of the wetland. Robust evidence on the net ‘storage’ or ‘removal’ of the entirety of the nutrient load entering the
wetland is essential to support effective policy and decision-making on whether they are the correct solution for eutrophication control.
Here, we:
1. Outline the processes controlling nutrient cycling in wetlands.
2. Offer a case study of a natural wetland, demonstrating its spatial (in terms of nutrient cycling) and temporal variability in cycling and
exporting accumulated nutrient loads to adjacent waters.
3. Present evidence on the bioavailability of dissolved and particulate nutrient fractions which, in many studies on wetlands as mitigation
features, are not measured at all.
4. Disprove the assumption (incorrect) in many mitigation efforts that only the inorganic nutrient fractions are bioavailable and cause
eutrophication impacts in freshwaters and demonstrate the need to take all nutrient fractions into account in policy and practice.
5. Provide a case study based on in-depth and holistic analysis of nutrient cycling and export in the Cromhall Constructed Wetland, owned
by Wessex Water and originally designed for the removal of phosphorus at a small rural water treatment centre.
Finally, we offer reflections on directions for future research which may assist in increasing nutrient removal potential in constructed wetlands
and summarise their longer-term limitations.
| Original language | English |
|---|---|
| Pages | 1-37 |
| Number of pages | 37 |
| DOIs | |
| Publication status | Unpublished - 2 Aug 2024 |