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- Title
Role of Lakes, Flood, and Low Flow Events in Modifying Catchment‐Scale DOC:TN:TP Stoichiometry and Export.
- Authors
Fasching, Christina; Boodoo, Kyle S.; Yao, Huaxia; Rusak, James A.; Xenopoulos, Marguerite A.
- Abstract
The balance of organic carbon (OC), nitrogen (N) and phosphorus (P) plays a crucial role in determining the processing, retention, and movement of these solutes across the aquatic continuum. Floods and droughts can significantly alter the quantity and ratios of OC:N:P export within inland waters, but how these ratios change, and are coupled within watersheds that integrate rivers and lakes, is not well known. We investigated the stoichiometry and export of dissolved organic carbon (DOC), total N (TN) and total P (TP) in two lake watersheds (10 inflows, 2 outflows) in the southern Boreal Shield over a 37‐year period. Although DOC, TN, and TP concentration behaved similarly, DOC:TN:TP ratios varied seasonally, strongly modulated by stream discharge. DOC:TN, DOC:TP and TN:TP export initially increased rapidly with increasing discharge, peaking at 10%–20% exceedance of the annual discharge for DOC:TP and TN:TP ratios, indicating a rapid depletion of catchment OC sources. Both flood and low flow events resulted in lower DOC:TN and lower DOC:TP export—thereby increasing the relative contributions of stream TN and TP. Consequently, elevated annual discharge coupled with infrequent but high floods and periods of low flow events increased the contributions of TN and TP relative to DOC. Overall, the lakes retained DOC, while increasing TN relative to TP. Nonetheless, the flow regime played a role in modulating nutrient retention in the lakes, likely due to changes in residence time, and the interplay of physical, photochemical, and biological degradation processes. Plain Language Summary: How floods and droughts affect the relationship between organic carbon (OC) and nitrogen and phosphorus in terms of their alteration, removal from, or storage within, river and lake environments is not well known. We investigated two lake watersheds with their 10 inflowing and 2 outflowing streams over 37 years. The ratios of the OC to nutrients changed seasonally and were affected by intra‐annual stream flow variability. Slightly higher than average flows (10%–20% higher) initially increased the amount of OC that was exported from the watershed compared to nitrogen and phosphorus, but this export was notably lower during low flows and floods. This highlights the effects of extremely high and low flows, resulting in increased nitrogen and phosphorus in the streams. Internal processing by lakes generally decreased OC, while adding nitrogen relative to phosphorus, however the lakes retained less OC and phosphorus when the number of annual floods increased. This is important as the frequency and intensity of floods and droughts are predicted to increase in the future which may change how nutrients are altered and removed along the inland‐marine aquatic continuum. These potential changes could impact aquatic ecosystems and the ecosystem services they provide. Key Points: Our long‐term data set provides a robust perspective on patterns in watershed‐scale stoichiometry and organic carbon and nutrient transportFlow regimes (floods and periods of low flow) are critical in shaping nutrient and organic carbon stoichiometry in aquatic ecosystemsLakes play an important role in nutrient and organic carbon removal within a stream network
- Subjects
BODIES of water; DISSOLVED organic matter; LAKES; STOICHIOMETRY; STREAMFLOW; FLOODS; DROUGHTS; WATERSHEDS
- Publication
Water Resources Research, 2024, Vol 60, Issue 3, p1
- ISSN
0043-1397
- Publication type
Article
- DOI
10.1029/2023WR034839