Limited evidence for spatial patterns of denitrification in tidal freshwater forested wetlands (TFFWs), seemingly due to high spatial variability in the process, is surprising considering the various spatial gradients of its biogeochemical and hydrogeomorphic controls in these ecosystems. Because certain physical environmental gradients may be useful for the prediction of denitrification in TFFWs, we measured denitrification and ecosystem attributes in hummock-hollow microtopography of TFFWs along longitudinal riverine positions (upper, middle, and lower tidal river sites, and nearby upstream nontidal forested floodplains) of the adjoining Pamunkey and Mattaponi Rivers, Virginia. We tested differences by river, site, and plot in denitrification enzyme activity (DEA) and substrate limitations of denitrification potential (DP). The Pamunkey River carries greater river nitrate concentrations, and we found less nitrate limitation of DP and greater soil nitrate in hollows of this river. DEA in tidal hummocks was positively correlated with soil organic matter, nitrogen, and carbon, with the highest rates in lower tidal sites. Hummocks also promoted greater oxygen-controlled substrate limitation of DP, whereby experimental aeration stimulated DP under subsequent inundation more in hummocks than hollows. Additionally, tidal sites had greater DEA than nontidal sites, inferred to be caused by a combination of higher moisture, organic, and nutrient content. Our results indicate that the increasing nitrogen concentrations in these rivers will increase denitrification more on the Mattaponi River by alleviating its greater nitrogen limitation compared to the Pamunkey River, and modification to sedimentation, inundation, or microtopography from sea level rise may alter denitrification gradients in TFFWs and upstream low-elevation nontidal floodplains.

中文翻译：

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潮汐淡水森​​林湿地的反硝化潜能模式

潮汐淡水森​​林湿地（TFFWs）中反硝化的空间模式的有限证据，似乎是由于该过程中的高度空间变异性，考虑到这些生态系统中生物地球化学和水文地貌控制的各种空间梯度，令人惊讶。因为某些物理环境梯度可能对预测TFFW的反硝化作用有用，所以我们在沿纵向河流位置（上，中，下潮汐河站点以及附近上游非潮汐森林泛滥平原）的TFFW的吊床空心微地形图中测量了反硝化作用和生态系统属性），毗邻弗吉尼亚州的Pamunkey和Mattaponi河。我们通过反硝化酶活性（DEA）和反硝化潜力（DP）的底物限制，按河流，地点和地块测试了差异。帕蒙基河中的硝酸盐浓度较高，我们发现该河中空区的硝酸盐局限性较小，而土壤硝酸盐含量较高。潮汐小丘的DEA与土壤有机质，氮和碳呈正相关，在低潮位点的发生率最高。吊床还促进了DP的更大的受氧控制的底物限制，因此，在随后的淹没条件下，实验通气对DP的刺激比对空心的刺激更大。此外，潮位比非潮位具有更大的DEA，这是由于较高的水分，有机物和营养成分共同导致的。我们的结果表明，与帕蒙基河相比，这些河流中不断增加的氮浓度将减轻其对氮的更大限制，从而进一步增加马塔波尼河的反硝化作用，