applying the n-mass balance model for visualizing biological productivity zones in narragansett bay, rhode island

Integrated Visualization of Biogeochemical Data for Nutrient Management

Primary productivity, the production of organic compounds by phytoplankton, fuels ecosystem food webs, and is important for understanding the system&#39;s function in response to environmental changes1,2. Estuarine primary productivity is also closely linked to eutrophication which is defined as excessive nutrients in the ecosystem1, causing several harmful consequences in the coastal regions, such as an overgrowth of phytoplankton leading to large algal blooms and subsequent hypoxia3,4. Importantly, primary productivity in estuaries is highly dependent on the riverine nutrient loading, particularly nitrogen concentrations, which are the typical limiting nutrient in most temperate ocean ecosystems5,6. However, an estimation of the extent of riverine nitrogen impacts in coastal areas remains challenging.
To estimate the estuarine primary productivity, a nitrogen (N) mass balance model is a useful tool to calculate nitrogen fluxes2. The N-mass balance model also provides an understanding of biological mechanisms beyond data observations, revealing information at the edges of different primary productivity zones7. Three different zones8, defined as brown, green, and blue zones, are particularly useful for predicting the impact of nutrient loading in hypoxic regions. The brown zone, defined as the nearest region of a river mouth, represents a high physical process, the green zone has high biological productivity, and the blue zone represents low biological process. The boundary of each zone depends on river flow, nutrient concentrations, and mixing rates8.
Narragansett Bay (NB) is a coastal, temperate estuary in Rhode Island, USA, supporting economic and ecological services and goods9,10,11, in which hypoxia has been consistently occurring. These hypoxic events, defined as the period of low dissolved oxygen (i.e., less than 2-3 mg of oxygen per liter), are particularly prevalent in July and August and are heavily impacted by riverine nitrogen loading during these months12. With an increase in primary production and hypoxia due to anthropogenic emissions of nutrients13, understanding the nitrogen inputs into NB is critical to managing and addressing coastal issues such as eutrophication and hypoxia. Thus, in this study, the rate of primary production in NB is calculated from the N-mass balance model using historically observed nutrient data, especially dissolved inorganic nitrogen (DIN). Based on the results of the N-mass balance model by converting to carbon units using the Redfield ratio, three different primary productivity zones were identified to visualize the extent of nitrogen influence from the river in NB. The model was then recreated into a 3D representation to better visualize the different zones. The products produced from this study can better inform nutrient management in NB in response to hypoxia and eutrophication. Further, results from this study are applicable to other coastal regions to visualize the effects of riverine transport on nutrients and primary productivity.

Author Spotlight: Understanding Riverine Nitrogen Impacts and Primary Productivity for Effective Nutrient Management

Visualization of Productivity Zones Based on Nitrogen Mass Balance Model in Narragansett Bay, Rhode Island

This study estimate the extension of the riverine nitrogen impacts and the primary productivity for better nutrient management in Narragansett Bay, the coastal area in the Rhode Island, USA. With increased primary production and hypoxia due to anthropogenic emissions of nutrients, understanding the nitrogen inputs into the bay is critical to managing and addressing coastal issues such as eutrophication and hypoxia. However, estimating the extent of nutrient inputs in coastal areas remains challenging.In this study, three different primary productivity zones were identified to visualize the extent of nitrogen influence from the river in the bay using the N mass balance model. This study also produced the results into a 3D representation for better visualization and nutrient management in the bay. As explained in the manuscript, the three theoretical zone can change over time depending on the nutrient concentration of the freshwater, mixing rate, and the river flow.As a result, the future work are the required to quantify these factors attributed to the flexibility of these regions better.

Applying the N-Mass Balance Model for Visualizing Biological Productivity Zones in Narragansett Bay, Rhode Island

To begin, after downloading the DIN data from the US Environmental Protection Agency, use Adobe Illustrator to divide Narraganset Bay into 15 boxes along its axis modified from the previous study. Using the given formula, calculate the mean concentration of DIN at each box. Calculate the potential primary production, or PPP rate, based on the N-Mass balance model by converting the net DIN removal to carbon units using the Redfield ratio.Save the PPP rate data of each box as a txt file. Then open the Ocean Data View software and load the PPP rate data by clicking the file menu and selecting open. In the metadata variable association window, click the associate variables box, latitude, longitude with station, latitude degrees north, and longitude degrees east.From the import window, click the OK button. Next, Right Click on the map and click zoom. Then drag the red box to zoom into the data area of the map, and click on Enter.From the view menu, click the one scatter window of the layout templates. Then Right Click In the sample panel and select derived variables. From the list of choices panel, under metadata, select latitude and click the add button.Repeat the same step for longitude and click OK.Next, by Right Clicking on the scatter window, select x variable as DRVD longitude degrees east. Similarly select y variable as DRVD latitude degrees north, and z variable as PPP in gram carbon per square meter per day. Select properties by Right Clicking on the scatter window and go to the display style option.Select the gridded field. Then move to the contours option and click the left Shift Button to make 0, 0.1 and two values only remain in the already defined panes of the left. Finally, click the OK button.Based on the contour plot from the software, define the edge of the brown, green, and blue zones in Narraganset Bay. Then using Adobe Illustrator, visualize these zones in the map. The N-Mass balance model identified three theoretical zones in Narraganset Bay for the summer.Brown zones had PPP rates greater than two gram carbon per square meter per day, indicating strong physical and biological processes, with high turbidity and limitation. Green zones had PPP rates between 0.1 to two gram carbon per square meter per day, displaying nutrient limitation and high primary production. Blue zones had PPP rates less than 0.1 to two gram carbon per square meter per day, representing low biological productivity.Physical frameworks were created using acrylic panels with LED lights to show overlaps of zone boundaries and sediment turbidity levels in each zone.

Research

JoVE Journal

Environment

Primary productivity in the coastal regions, linked to eutrophication and hypoxia, provides a critical understanding of ecosystem function. Although ...