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Streams in the southeastern United States Coastal Plains serve as an essential source of energy and nutrients for important estuarine ecosystems, and dissolved organic matter (DOM) exported from these streams can have profound impacts on the biogeochemical and ecological functions of fluvial networks. Here, we examined hydrological and temperature controls of DOM during low-flow periods from a forested stream located within the Coastal Plain physiographic region of Alabama, USA. We analyzed DOM via combining dissolved organic carbon (DOC) analysis, fluorescence excitation–emission matrix combined with parallel factor analysis (EEM-PARAFAC), and microbial degradation experiments. Four fluorescence components were identified: terrestrial humic-like DOM, microbial humic-like DOM, tyrosine-like DOM, and tryptophan-like DOM. Humic-like DOM accounted for ~70% of total fluorescence, and biodegradation experiments showed that it was less bioreactive than protein-like DOM that accounted for ~30% of total fluorescence. This observation indicates fluorescent DOM (FDOM) was controlled primarily by soil inputs and not substantially influenced by instream production and processing, suggesting that the bulk of FDOM in these streams is transported to downstream environments with limited in situ modification. Linear regression and redundancy analysis models identified that the seasonal variations in DOM were dictated primarily by hydrology and temperature. Overall, high discharge and shallow flow paths led to the enrichment of less-degraded DOM with higher percentages of microbial humic-like and tyrosine-like compounds, whereas high temperatures favored the accumulation of high-aromaticity, high-molecular-weight, terrestrial, humic-like compounds in stream water. The flux of DOC and four fluorescence components was driven primarily by water discharge. Thus, the instantaneous exports of both refractory humic-like DOM and reactive protein-like DOM were higher in wetter seasons (winter and spring). As high temperatures and severe precipitation are projected to become more prominent in the southeastern U.S. due to climate change, our findings have important implications for future changes in the amount, source, and composition of DOM in Coastal Plain streams and the associated impacts on downstream carbon and nutrient supplies and water quality.
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Green roof vegetation management alters potential for water quality and temperature mitigation
Abstract The global increase of urban impervious land cover poses a significant threat to the integrity of river ecosystems. Hence, it is critical to assess the efficiency of green roofs (GR) to mitigate the negative impacts of urbanization on river ecosystems, such as thermal surges and pollutants. In this study, we evaluated the ecohydrological behaviour of two fully established GR under differing management regimes at the Chicago Botanical Gardens from July to September 2019. The drainage outflow from a non‐vegetated roof, a managed GR (perennial native and non‐native plants) and an unmanaged GR (perennial natural prairie vegetation) were monitored, and thermal dynamics, dissolved organic matter (DOM) composition and nitrate concentration assessed. The managed GR runoff had a lower DOC concentration and less humic‐like DOM signal (SUVA254) compared to the unmanaged GR. In contrast, lower concentrations of nitrate and more recalcitrant DOM (less protein‐like compounds relative to humic‐like compounds) were associated with the unmanaged GR. The unmanaged GR also displayed a greater capacity to reduce thermal surges associated with storm events. Our study provides new information on the implications of GR management for water quality with particular relevance to the urban stream syndrome. Further, the impacts of GR management on the mitigation of thermal surges and DOM composition can help to improve future GR design, as these ecohydrological responses have been largely overlooked to date. Our findings can support future urban planning, particularly for scenarios where green infrastructures are used to mitigate the impacts of climate change on urban river ecosystems.
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- Award ID(s):
- 1848683
- PAR ID:
- 10445885
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecohydrology
- Volume:
- 14
- Issue:
- 6
- ISSN:
- 1936-0584
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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