The impact of a riparian wetland on streamwater quality in a recently afforested upland catchment
1994
Emmett, B.A. | Hudson, J.A. | Coward, P.A. | Reynolds, B.
The influence of a small remnant wetland on streamwater chemistry at the outflow of an afforested catchment has been investigated. The wetland reduced the volume weighted mean concentrations of a number of solutes. Stream solute loadings were calculated from chemical and flow data from two flumes situated above and below the wetland at the catchment outlet. The flow contribution from the wetland itself was estimated on an areal basis and combined with sampled chemistry to estimate solute fluxes. Streamwater dissolved nitrogen loading, equivalent to an input of 55 kg N ha-1 year-1, was reduced by 38% after flowing through the wetland. Reductions in streamwater loadings were also observed for phosphate (94%), total dissolved-P (42%), total monomeric aluminium (39%), total filtrable aluminium (21%), iron (54%), DOC (34%) and silica (21%). All other retention rates were within the original stream-water loading estimate errors. Retention of nitrogen was lower than expected, perhaps due to exhaustion of the wetland's immobilisation capacity by the large nitrogen loading in the streamwater entering the wetland from the surrounding land in combination with atmospheric loadings. Retention of nitrogen and other solutes was also reduced due to a prolonged period of low rainfall during the summer of 1989 which resulted in high concentration events of various elements from the wetland relative to concentrations at the wetland inflow.
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