This report constitutes the second phase to document the water quality benefits of a stream restoration in the coastal plain of North Carolina. This phase compares the pre-restoration and post-restoration states of the water quality and hydrochemical signature of ‘the canal’ at the Claridge nursery in Goldsboro, NC. We made the hypothesis that a robust way to quantify the
water quality benefits of this stream restoration was the use of cumulative nutrient load indicators. However, these indicators required the use of state-of-the-art instruments capable of capturing flow and water quality on a near continuous basis over the long term. After meticulous correction and all the necessary verifications, we were able to show that the restoration of the Claridge nursery canal, effectively creating a flowing wetland, was able to lower the nitrate loads by about 30% over three post-restoration consecutive years. This was accompanied by an overall carbon sequestration.
The seasonality of the nitrate retention suggests that much of the nitrate unaccounted for was associated with the growth of vegetation, either through plant uptake and/or through denitrification associated with the release of organic matter from dead vegetation and the exchange conditions that they provided in the channel and with the floodplain. Increased residence time associated with the aquatic vegetation working as a filter time likely increased the capacity of the stream to retain nitrate. The seasonality of the nitrate retention may suggest that shorter monitoring periods could be chosen to represent a ‘summer’ vs. a ‘winter’ effect. However, averaging these effects would not necessarily represent the effective benefits over the long term. Instead, we suggest that monitoring should focus on cumulative indicators used over the long term for projects forwhich there is a high potential for nutrient retention. Fewer projects may have to be monitored, but using the necessary investment.
