Habitat-Specific Solute Retention in Two Small Streams: An Intersite Comparison
Habitat-Specific Solute Retention in Two Small Streams: An Intersite Comparison
复制标题
两条小溪中特定栖息地的溶质保留：站点间比较
作者：
N. Munn;J. Meyer
我们测量了两条源头溪流对磷、硝酸盐、钙和溶解有机碳的吸收速率，一条在北卡罗来纳州的阿巴拉契亚山脉，另一条在俄勒冈州的喀斯喀特山脉。这两条河流的主要物理差异是母体地质和局部地貌结构。测定了1987年夏季不同地貌的20米河段低水平养分释放后的吸收速率。通过实验室实验评估了两条溪流沉积物对氮和磷的生物和非生物吸附的相对重要性。夏季，西流的硝态氮吸收速率较高(11.9gim-22min-1)，东流的硝态氮吸收速率较低(3.9Agm-2minm)。俄勒冈州的瓦砾坝段对N的截留率最高(最短吸收长度为17m)。相反，东部河流的可溶性活性磷(SRP)吸收速率较高(18.6Agm-2min)，主要是通过生物过程。东部河流卵石段(32m)、碎石坝段(35m)和露头岩段(40m)SRP吸收长度较短。这两条河流对SRP的吸收与沉积物粒度分数无关，而是与沉积物入渗速率和有机物质质量的组合有关。俄勒冈河的钙吸收长度较长(1278米)，而阿巴拉契亚河流的钙吸收长度较短(106米)。令人惊讶的是，在这段时间里，东溪对钙的保留比硝酸盐(对钙的吸收长度较短)更多。泥石坝极大地提高了溶解有机碳在两个溪流中的滞留量(东溪占总吸纳量的60%，西溪占81%)，但东溪的滞留量更大。根据地理位置和母体地质，俄勒冈州河流对磷的吸收速率较低，对硝酸盐的吸收速率较高；该地区的河流排出火山成因的集水区，并倾向于低N：P(原子；西溪为1.8)，表明潜在的N限制。流经花岗岩基岩的河流，如东溪，往往具有较低的磷有效性(N：P=15.5)。实验室和野外测量的综合结果表明，在东溪，对磷吸收的强烈生物控制加上高磷需求，导致磷吸收长度相对较短，磷螺旋对生态系统动力学的影响较大。在西溪，生物对氮素吸收的强烈控制和强烈的氮素需求导致了较短的氮素吸收长度。尤其是在同时保留了FPOM和CPOM的羽化木材站点，产生了高N需求(缩短N螺线)。
We measured uptake rates of phosphorus, nitrate, calcium, and dissolved organic carbon within two headwater streams, one in the Appalachian mountains of North Carolina and the other in the Cascade range of Oregon. The major physical differences between these two streams are parent geology and local geomorphic structure. Uptake rates were measured following low-level nutrient releases during summer 1987 in 20-m reaches with different geomorphology. The relative importance of biotic vs. abiotic sorption of nitrogen and phosphorus by sediments from the two streams was assessed by laboratory experiments. Nitrate-N uptake rates were high for the western stream (11.9 g im-22 min-1) and low for the eastern stream (3.9 Ag m-2 minm) during the summer. The debris dam reaches in Oregon were the most retentive of N (shortest uptake length of 17 m). Conversely, sol- uble reactive phosphorus (SRP) uptake rates were higher for the eastern stream (18.6 Ag m- 2 min), primarily through biotic processes. SRP uptake lengths were short for the cobble (32 m), debris dam (35 m), and rock outcrop (40 m) reaches in the eastern stream. Uptake of SRP in either stream was not related to sediment size fraction but rather to a combination of sediment infiltration rates and quality of organic material. Calcium (Ca) uptake lengths were long in the Oregon stream (1278 m) but short in the Appalachian stream (106 m). Surprisingly, the eastern stream was more retentive of Ca than nitrate (shorter uptake lengths for Ca) during this time period. Debris dams greatly enhanced retention of dissolved organic carbon in both streams (60% of all uptake in the eastern stream and 81 % in the western stream), although retention was greater in the eastern stream. The lower uptake rate of phosphorus and higher uptake rate of nitrate in the Oregon stream were expected based on geographic location and parent geology; streams in this area drain catchments of volcanic origin and tend to have low N:P (atomic; 1.8 for the western stream) ratios, indicating potential N limitation. Streams flowing over granitic bedrock, such as the eastern stream, tend to have lower P availability (N:P = 15.5). The combined results of laboratory and field measurements indicate that in the eastern stream, strong biotic control of P uptake coupled with high P demand result in relatively short P uptake lengths and a strong impact of P spiraling on ecosystem dynamics. In the western stream, strong biotic control of N uptake combined with strong N demand result in short N uptake lengths. This is especially true at sites of downed timber that retain both FPOM and CPOM, creating a high N demand (shortening N spirals).