Center for Water Supply Studies, Texas A&M University-Corpus Christi, Corpus Christi, TX 78412, USA.
Harte Research Institute for Gulf of Mexico Studies, Texas A&M University-Corpus Christi, Corpus Christi, TX 78412, USA.
Sci Total Environ. 2021 Feb 10;755(Pt 2):142574. doi: 10.1016/j.scitotenv.2020.142574. Epub 2020 Sep 29.
Nutrient budgets in semi-arid estuaries, with ephemeral freshwater inflows and limited nutrient sources, are likely incomplete if contributions from submarine groundwater discharge (SGD) are not included. Here, the relative importance of saline/recirculated SGD-derived nutrient fluxes spatiotemporal variability to the overall nutrient budget is quantified for Nueces Bay, Texas, U.S.A., across hydroclimatic conditions ranging from drought to normal, to flood. On average, 67% of the variance in water quality is due to temporal differences while 16% is explained by spatial differences. Principal component analysis (PCA) reveals three principal components: freshwater inflow (PC1 28.8%), saline/recirculated SGD and recycled nitrogen (PC2 15.6%), and total SGD and "new" nitrogen (PC3 11.2%). Total SGD porewater fluxes ranged from 29.9-690.3 mmol∙md for ammonium, 0.21-18.7 mmol∙md for nitrite+nitrate, 3.1-51.3 mmol∙md for phosphate, 57.1-719.7 mmol∙md for silicate, and 95.9-36,838.5 mmol∙md for dissolved organic carbon. Total and saline/recirculated SGD fluxes were on average 150-26,000 and 5.8-466 times, respectively, greater than surface runoff fluxes across all seasons. Nitrogen (N) enrichment in porewater occurs near the agricultural fields because of soil N flushing and percolation to groundwater, which facilitates N-rich groundwater fluxes. There were substantial "new" N inputs from terrestrial groundwater following precipitation while saline/recirculated SGD of recycled N accounts for only <4% of total SGD inputs. The "new" N inputs occur in the river and river mouth during flooding, and near the north shore where topography and hydraulic gradients are steeper during drought. Thus, while significant inputs of N may be associated with atmospheric deposition, or remineralization in the porewater, groundwater is the highest contributor to the nutrient budget in Nueces Bay. This result implies that nutrient management strategies should focus on land-use practices to reduce N contamination of shallow groundwater and subsequent contamination of estuaries.
在半干旱河口，如果不包括海底地下水排泄 (SGD) 的贡献，营养物收支可能是不完整的。在这里，我们量化了德克萨斯州纽埃西斯湾 (Nueces Bay) 在从干旱到正常到洪水的各种水文气候条件下，盐度/再循环 SGD 衍生养分通量的时空变异性对整体养分收支的相对重要性。平均而言，水质变化的 67%是由于时间差异，而 16%是由空间差异解释的。主成分分析 (PCA) 揭示了三个主要成分：淡水流入 (PC1，占 28.8%)、盐度/再循环 SGD 和再循环氮 (PC2，占 15.6%)，以及总 SGD 和“新”氮 (PC3，占 11.2%)。总 SGD 孔隙水通量范围为铵盐 29.9-690.3 mmol·md-1、亚硝酸盐+硝酸盐 0.21-18.7 mmol·md-1、磷酸盐 3.1-51.3 mmol·md-1、硅酸盐 57.1-719.7 mmol·md-1 和溶解有机碳 95.9-36,838.5 mmol·md-1。总 SGD 和盐度/再循环 SGD 通量在所有季节的平均值分别比地表径流量高出 150-26,000 倍和 5.8-466 倍。由于土壤氮冲刷和渗滤到地下水，导致近农田地区孔隙水氮富化，促进了富氮地下水通量。降水后，地下水从陆地带来大量“新”氮输入，而循环氮的盐度/再循环 SGD 仅占总 SGD 输入的<4%。“新”氮输入发生在洪水期间的河流和河口，以及在旱季地形和水力梯度较陡的北岸。因此，尽管大气沉积或孔隙水中的再矿化可能与大量氮输入有关，但地下水是纽埃西斯湾养分收支的最大贡献者。这一结果意味着，养分管理策略应侧重于减少浅地下水氮污染和随后对河口污染的土地利用实践。
