Department of Biology and North Carolina Center for Biodiversity, East Carolina University, Greenville, NC 27858, USA.
Sci Total Environ. 2013 Jan 15;443:267-77. doi: 10.1016/j.scitotenv.2012.10.068. Epub 2012 Nov 28.
Research into the buffering mechanisms and ecological consequences of acidification in tropical streams is lacking. We have documented seasonal and episodic acidification events in streams draining La Selva Biological Station, Costa Rica. Across this forested landscape, the severity in seasonal and episodic acidification events varies due to interbasin groundwater flow (IGF). Streams that receive IGF have higher concentrations of solutes and more stable pH (~6) than streams that do not receive IGF (pH ~5). To examine the buffering capacity and vulnerability of macroinvertebrates to short-term acidification events, we added hydrochloric acid to acidify a low-solute, poorly buffered (without IGF) and a high-solute, well buffered stream (with IGF). We hypothesized that: 1) protonation of bicarbonate (HCO(3)(-)) would neutralize most of the acid added in the high-solute stream, while base cation release from the sediments would be the most important buffering mechanism in the low-solute stream; 2) pH declines would mobilize inorganic aluminum (Ali) from sediments in both streams; and 3) pH declines would increase macroinvertebrate drift in both streams. We found that the high-solute stream neutralized 745 μeq/L (96% of the acid added), while the solute poor stream only neutralized 27.4 μeq/L (40%). Protonation of HCO(3)(-) was an important buffering mechanism in both streams. Base cation, Fe(2+), and Ali release from sediments and protonation of organic acids also provided buffering in the low-solute stream. We measured low concentrations of Ali release in both streams (2-9 μeq/L) in response to acidification, but the low-solute stream released double the amount Ali per 100 μeq of acid added than the high solute stream. Macroinvertebrate drift increased in both streams in response to acidification and was dominated by Ephemeroptera and Chironomidae. Our results elucidate the different buffering mechanisms in tropical streams and suggest that low-solute poorly buffered streams might be particularly vulnerable to episodic acidification.
对热带溪流酸化的缓冲机制和生态后果的研究还很缺乏。我们记录了流经哥斯达黎加拉塞尔瓦生物站的溪流的季节性和间歇性酸化事件。在这片森林景观中，由于流域间地下水流动 (IGF) 的存在，季节性和间歇性酸化事件的严重程度有所不同。接收 IGF 的溪流具有更高的溶质浓度和更稳定的 pH 值（约 6），而不接收 IGF 的溪流的 pH 值（约 5）则较低。为了研究大型无脊椎动物对短期酸化事件的缓冲能力和脆弱性，我们向低溶质、缓冲能力差（没有 IGF）和高溶质、缓冲能力好（有 IGF）的溪流中添加盐酸来酸化它们。我们假设：1）碳酸氢根离子（HCO(3)(-)) 的质子化作用会中和高溶质溪流中添加的大部分酸，而底质中基阳离子的释放将是低溶质溪流中最重要的缓冲机制；2）pH 值的下降将使两种溪流中的无机铝（Ali）从沉积物中释放出来；3）pH 值的下降将增加两种溪流中的大型无脊椎动物漂流。我们发现，高溶质溪流中和了 745 μeq/L（添加酸的 96%），而溶质贫乏的溪流仅中和了 27.4 μeq/L（40%）。HCO(3)(-) 的质子化作用是两种溪流中重要的缓冲机制。底质中基阳离子、Fe(2+) 和 Ali 的释放以及有机酸的质子化作用也为低溶质溪流提供了缓冲。我们在两种溪流中都测量到了低浓度的 Ali 释放（2-9 μeq/L），但低溶质溪流每添加 100 μeq 的酸，释放的 Ali 量是高溶质溪流的两倍。酸化作用导致两种溪流中的大型无脊椎动物漂流增加，以蜉蝣目和摇蚊科为主。我们的研究结果阐明了热带溪流的不同缓冲机制，并表明低溶质、缓冲能力差的溪流可能特别容易受到间歇性酸化的影响。
