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Stable isotopes: A tool for detecting nitrogen cycle processes in laboratory microcosm experiments.

機譯：穩(wěn)定同位素：在實驗室微觀實驗中檢測氮循環(huán)過程的工具。

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Salt marsh estuaries are valuable habitats that perform important functions such as providing habitat and nursery areas for commercially important species, mitigating the effects of storms on coastal communities, and filtering nutrients and other contaminants from water entering the coast. Anthropogenic nitrogen (N) inputs have the potential to degrade the quality of salt marsh estuaries and affect their ability to perform these valuable functions. 15N has been used in field studies at natural abundance and in laboratory studies using an enriched tracer to study N cycle processes occurring in coastal ecosystems. The purpose of this study was to adapt N stable isotope natural abundance techniques to laboratory denitrification assays to examine other N cycle processes that may be occurring. This technique was then used to examine the effects of anthropogenic N loading on N cycle processes in salt marsh estuaries by comparing the results from two study sites, one receiving anthropogenic N inputs from a nearby golf course and one in an undeveloped area. Potential denitrification rates at both sites were directly related to the amount of nitrate (NO3-) added to the overlying water column and potential denitrification rates were higher at the impacted site than the unimpacted site regardless of water column NO3- concentration (0, 700 or 1400 microg NO3--N). Potential dissimilatory NO3- reduction to ammonium (NH4+) (DNRA) rates measured through mass balance did not appear to vary by either NO3- addition or study site. In most instances measured NH4+ accumulation in microcosms was small, but the delta15N of NH4 + changed significantly with time suggesting that microbial assimilation and sediment organic matter (SOM) mineralization were occurring even when N species concentrations were stable. However quantifying the exact proportions of microbial assimilation and SOM mineralization using the stable isotope data was not possible because the fractionation factors of these processes were unknown.
機譯：鹽沼河口是有價值的棲息地，具有重要的功能，例如為商業(yè)上重要的物種提供棲息地和育苗區(qū)，減輕風暴對沿海社區(qū)的影響，并過濾進入海岸的水中的養(yǎng)分和其他污染物。人為氮輸入可能會降低鹽沼河口的質(zhì)量并影響其執(zhí)行這些寶貴功能的能力。 15N已用于自然豐度的野外研究和實驗室研究中，使用了豐富的示蹤劑來研究沿海生態(tài)系統(tǒng)中發(fā)生的N個循環(huán)過程。這項研究的目的是使N穩(wěn)定同位素自然豐度技術(shù)適應實驗室的反硝化分析，以檢查可能發(fā)生的其他N循環(huán)過程。然后，通過比較兩個研究地點的結(jié)果，使用該技術(shù)來檢查鹽沼河口中人為氮負荷對N循環(huán)過程的影響，其中一個研究地點從附近的高爾夫球場接收人為氮輸入，另一個在未開發(fā)地區(qū)接受。兩個位點的潛在反硝化率都與上覆水柱中硝酸鹽（NO3-）的含量直接相關(guān)，無論水柱中的NO3-濃度如何（0、700或700），受影響位點的潛在反硝化率均高于未受影響位點。 1400微克NO3--N）。通過質(zhì)量平衡測得的潛在異化NO3-還原為銨（NH4 +）（DNRA）的速率似乎不會因添加NO3-或研究地點而變化。在大多數(shù)情況下，測得的NH4 +在微觀世界中的積累很小，但是NH4 +的δ15N隨時間發(fā)生顯著變化，這表明即使N種濃度穩(wěn)定，微生物的同化作用和沉積物有機物（SOM）也會發(fā)生礦化作用。然而，由于這些過程的分餾因子未知，因此無法使用穩(wěn)定的同位素數(shù)據(jù)來量化微生物同化和SOM礦化的確切比例。

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