Name: understanding dissolved organic matter biogeochemistry through in situ nutrient manipulations in stream ecosystems
Uploaded: 2016-10-29T15:00:00
Description: Watch this Scientific Journal Video about Understanding Dissolved Organic Matter Biogeochemistry Through In Situ Nutrient Manipulations in Stream Ecosystems at JoVE.com

The authors acknowledge the Water Quality Analysis Laboratory at the University of New Hampshire for assistance with sample analysis. The authors also thank two anonymous reviewers whose comments have helped to improve the manuscript. This work is funded by the National Science Foundation (DEB-1556603). Partial funding was also provided by the EPSCoR Ecosystems and Society Project (NSF EPS-1101245), New Hampshire Agricultural Experiment Station (Scientific Contribution #2662, USDA National Institute of Food and Agriculture (McIntire-Stennis) Project (1006760), the University of New Hampshire Graduate School, and the New Hampshire Water Resources Research Center.

1. Identifying and Characterizing the Ideal Experimental Stream Reach
<ol>
	<li>Ensure that experimental stream reaches are long enough to promote complete mixing of solutes11 and long enough where biological uptake can occur. Reach lengths can vary among streams and experiments. In small first-order headwater streams, reach length may vary from 20-150 m (or longer if the system requires it) depending on discharge and other physical properties of the stream.
	<ol>
		<li>Exclude large pools from experimental ...

<ol>
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The objective of the nutrient pulse method, as presented here, is to characterize and quantify the response of the highly diverse pool of ambient stream water DOM across a dynamic range of an added inorganic nutrient. If the added solute sufficiently increases the concentration of the reactive solute, a large inferential space can be created to understand how the biogeochemical cycling of DOM is linked to nutrient concentrations. This nutrient pulse approach is ideal as it involves none of the machinery associated with p...

Dissolved organic matter (DOM) provides an important energy and nutrient source to freshwater ecosystems and is defined as organic matter that passes through a 0.7 &#181;m filter. Within aquatic ecosystems, DOM can also influence light attenuation and metal complexation. DOM is a highly diverse and heterogeneous mixture of organic compounds with various functional groups, as well as essential nutrients such as nitrogen (N) and phosphorous (P). While the term &#34;DOM&#34; describes the entire pool including its C, N and P components, its concentration is measured as dissolved organic carbon (DOC). The inherent molecular complexity of the DOM pool however, creates challenges to its study. For example, there is no direct way to measure the fraction of the total DOM pool comprised of organic nutrients such as dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP). Instead, the concentration of organic nutrients must be determined by difference (e.g. [DON] = [total dissolved nitrogen] - [dissolved inorganic nitrogen]).
Adding a realistic DOM amendment to a stream is difficult due to the diversity of the ambient DOM pool. Previous studies have added single carbon sources (e.g. glucose, urea1) or a particular source such as leaf litter leachate2 to manipulate concentrations in the field. However, these sources are not particularly representative of the ambient DOM pool. Trying to refine or concentrate ambient DOM for subsequent experimentation is also wrought with difficulties including the loss of certain fractions (e.g. highly labile components) during processing. As a result, it is difficult to understand the controls on the ambient DOM pool as we currently do not possess any method to directly manipulate the ambient DOM pool. However, since the biogeochemistry of DOM is linked to nutrients commonly found in the environment (e.g. nitrate [NO3-]3), we can add other solutes to stream ecosystems and measure the response of the DOM pool to these manipulations. By examining how the DOM pool responds to a wide range of experimentally imposed nutrient concentrations we hope to gain better insight into how DOM responds to fluctuating environmental conditions.
One method commonly used in stream biogeochemistry is the nutrient addition method. Nutrient addition experiments have traditionally been used to understand uptake kinetics or the fate of the added solute4,5,6,7. Nutrient additions can be short-term on the hr6 to day scale4, or longer-term manipulations over the course of multiple years8. Nutrient additions can also include isotopically labelled nutrients (e.g. 15N-NO3-) to trace added nutrient through biogeochemical reactions. However, isotope-based studies are often expensive and require challenging analyses (e.g. digestions) of the multiple benthic compartments where isotopically-labeled nutrients may be retained. Recent experimentation has revealed the utility of short-term nutrient pulses to elucidate the controls on non-added and ambient solutes such as DOM9,10, revealing a new way by which to examine real-time in situ biogeochemical reactions. Here we describe and demonstrate the key methodological steps to conducting short-term nutrient pulses with the objective of understanding the coupled biogeochemistry of C and N and specifically the controls on the highly diverse DOM pool. This easily reproducible method involves adding a nutrient pulse to an experimental stream reach and measuring changes in the concentration of both the manipulated solute and the response variable of interest (e.g. DOC, DON, DOP). By directly manipulating nutrient concentrations in situ we are able to indirectly alter the DOM pool and examine how DOM concentration changes across a dynamic range of nutrient concentrations10.

<table border="0" cellpadding="0" cellspacing="0" width="593">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Sodium Nitrate</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Sodium Chloride</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td>Store purchased table salt can be used as well, however, it does contain trace levels of impurities</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Whatman GFF glass-fiber filters</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">BD Filtering Syringe</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">EMD Millipore Swinnex Filter Holders</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Syringe stop-cock</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td></td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:216px;">YSI Multi-parameter probe</td>
			<td style="width:91px;">Yellow Springs International</td>
			<td>556-01</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Wide mouth HDPE 125 ml bottles</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">60 ml HDPE bottles</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">20 L bucket</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Field measuring tape</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Lab labeling tape</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Stir stick</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Cooler</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Sharpie pen</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Field notebook</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Tweezers</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Zip-lock bags</td>
			<td style="width:91px;">Any</td>
			<td style="width:119px;">Any</td>
			<td></td>
		</tr>
	</tbody>
</table>

understanding dissolved organic matter biogeochemistry through in situ nutrient manipulations in stream ecosystems

Dissolved organic matter (DOM) is a highly diverse mixture of molecules providing one of the largest sources of energy and nutrients to stream ecosystems. Yet the in situ study of DOM is difficult as the molecular complexity of the DOM pool cannot be easily reproduced for experimental purposes. Nutrient additions to streams however, have been shown to repeatedly alter the in situ and ambient DOM pool. Here we demonstrate an easily replicable field-based method for manipulating the ambient pool of DOM at the ecosystem scale. During nutrient pulse experiments changes in the concentration of both dissolved organic carbon and dissolved organic nitrogen can be examined across a wide-range of nutrient concentrations. This method allows researchers to examine the controls on the DOM pool and make inferences regarding the role and function that certain fractions of the DOM pool play within ecosystems. We advocate the use of this method as a technique to help develop a deeper understanding of DOM biogeochemistry and how it interacts with nutrients. With further development this method may help elucidate the dynamics of DOM in other ecosystems.

<img alt="Figure 3" src="/files/ftp_upload/54704/54704fig3.jpg" /> 
Figure 3: Example Results from Nitrate (NO3-) Additions with Dissolved Organic Nitrogen (DON) as the Response Variable. Analyses are linear regressions. Asterisks represent statistical significance at &#945; = 0.05. Note the dynamic range in NO3- concentration that was achieved with the nutrient pulse method. Different pane...

Watch this Scientific Journal Video about Understanding Dissolved Organic Matter Biogeochemistry Through In Situ Nutrient Manipulations in Stream Ecosystems at JoVE.com

Understanding Dissolved Organic Matter Biogeochemistry Through In Situ Nutrient Manipulations in Stream Ecosystems

Dissolved organic matter provides an important source of energy and nutrients to stream ecosystems. Here we demonstrate a field-based method to manipulate the ambient pool of dissolved organic matter in situ through easily replicable nutrient pulses.

Understanding Dissolved Organic Matter Biogeochemistry Through In Situ Nutrient Manipulations in Stream Ecosystems

Dissolved organic matter (DOM) is a highly diverse mixture of molecules providing one of the largest sources of energy and nutrients to stream ecosystems. ...

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