Nutrient Retention and the Problem of Hydrologic Disconnection in Streams and Wetlands
Nutrient Retention and the Problem of Hydrologic Disconnection in Streams and Wetlands
复制标题
溪流和湿地的养分保留和水文断层问题
作者：
S. Powers;Robert A. Johnson;E. Stanley
一些水生系统具有不成比例的高营养物质处理速率，可能对河网内的营养物质保留很重要。然而，这些生物地球化学热点的贡献还取决于水停留时间和系统内的水文联系。我们在美国威斯康辛州北部的溪流和流经湿地河段的硝酸盐（NO3−）吸收的比较研究中检查了这些因素的平衡。实验设计比较了不同水平上的NO3−吸收率：生态系统水平，由形态不同的河段（慢，低平均水速；REF，参考，或更高平均水速）组成；亚生态系统水平，对于由形态对比区（TS，暂存区；MC，主河道区）组成的子河段。SLOW亚段的生态系统水平吸收率（K, t−1）平均低45%，表明径流湿地的吸收率相对于溪流较低。4个最大的K值（总n = 24）也出现在REF子河段。TS:MC吸收速率变化（范围0.1-6.0），但MC带始终占生态系统NO3−吸收的大部分。反过来，TS区吸收速率与TS - mc水文连接强度（α或Fmed）之间的权衡限制了TS的影响。对已发表的水文参数集进行的额外建模表明，在溶质释放方法（米到公里，小时到天）的尺度上，强MC优势吸收（占总吸收量的75%）在溪流和河流中很常见。我们的研究结果强调，水生营养保留是营养吸收效率、水停留时间以及营养源和汇之间水文联系强度平衡的结果。这种平衡限制了水文非连通生物群对营养物质运输的影响，适用于不同类型和规模的生态系统。
Some aquatic systems have disproportionately high nutrient processing rates, and may be important to nutrient retention within river networks. However, the contribution of such biogeochemical hot spots also depends on water residence time and hydrologic connections within the system. We examined the balance of these factors in a comparative study of nitrate (NO3−) uptake across stream and flow-through wetland reaches of northern Wisconsin, USA. The experimental design compared NO3− uptake at different levels: the ecosystem level, for reaches (n = 9) consisting of morphologically contrasting subreaches (SLOW, low mean water velocity; REF, reference, or higher mean water velocity); the sub-ecosystem level, for subreaches consisting of morphologically contrasting zones (TS, transient storage zone; MC, main channel zone). SLOW subreaches had 45% lower ecosystem-level uptake rate (K, t−1) on average, indicating reduced uptake efficiency in flow-through wetlands relative to streams. The four largest K values (total n = 24) also occurred in REF subreaches. TS:MC uptake rate varied (range 0.1–6.0), but MC zones consistently accounted for most NO3− uptake by the ecosystem. In turn, TS influence was limited by a tradeoff between TS zone uptake rate and the strength of TS–MC hydrologic connection (α or Fmed). Additional modeling of published hydrologic parameter sets showed that strong MC dominance of uptake (>75% of total uptake), at the scale of solute release methods (meters to kilometers, hours to days), is common among streams and rivers. Our results emphasize that aquatic nutrient retention is the outcome of a balance involving nutrient uptake efficiency, water residence time, and the strength of hydrologic connections between nutrient sources and sinks. This balance restricts the influence of hydrologically disconnected biota on nutrient transport, and could apply to diverse ecosystem types and sizes.