Abstract—The West and Rhode Rivers (WRR), two mezohaline sub-estuaries of the Chesapeake Bay, contain a total volume of 25 million m³ of water and have a 78 km² watershed. Due to local runoff and the excess nutrients and total suspended solids (TSS) entering the WRR from the Chesapeake Bay, water quality in these sub-estuaries has steadily declined over the last forty years. Models and data analysis have shown that as much as 90% of nutrient and TSS inputs to the WRR enter via inflowing tidal water from the Chesapeake Bay; therefore, community outreach efforts are predicted to have little impact on water quality.

An oyster aquaculture system has been found to be potentially sustainable and capable of decreasing turbidity within the WRR. The oysters act as water filters which filter nutrients and TSS. Three alternatives have been proposed: Larvae stage aquaculture, Seed stage aquaculture, and Spat-on-shell aquaculture. Three models were used in conjunction in order to evaluate these alternatives; an oyster growth model to simulate the growth rate of oysters within the varying conditions of the WRR, a 2D Tidal Mixing Model (2DTMM) to simulate the dynamic flow of nutrients within the WRR, and a business model to simulate the sustainability of an oyster aquaculture enterprise.

An analysis of cost versus utility (water quality improvement, sustainability, and public approval) shows that the INSERT SOLUTION would be the most cost-effective alternative.

I. INTRODUCTION

HE West and Rhode rivers are two sub-estuaries of the Chesapeake Bay which contain 26 million cubic meters

of water. The watershed covers 78 square kilometers and has an average depth of 2 meters. Fresh water flows into the Chesapeake Bay from the Susquehanna River and is mixed with salt water flowing up from the Atlantic. The rivers undergo constant fluctuations in the salinity of the water.

T

Excess sediment and nutrients, which mostly flow in to the sub-estuaries with the tide, as well as run-off sediments from the land, have over time increased turbidity which has caused a decrease in the secchi depth of the rivers. Secchi depth is the measure of the clarity of water. Due to the low secchi depth, under water vegetations, also known as sub aquatic vegetation (SAV), are not receiving proper sunlight and oxygen to sustain life. In 2010, no under-water grasses were found in the rivers [1].

There is a correlation between the chlorophyll level and nitrogen level in the water. Nitrogen serves as food for algae, thus increasing the level of chlorophyll in the water as

the level of nitrogen decreases. Though algae may seem like a good source of filtration in the rivers due to the ingestion of nitrogen, algae blooms are one of the contributors to turbidity in the rivers. Once the algae have reached a large growth, they start to die off and oxidize, thereby reducing the dissolved oxygen level in the water.

As an organism that feeds off of nutrients and sediments in the water, oysters provide a natural form of filtration for the rivers. Once a populous resource in the region, they are now virtually non-existent in the West and Rhode Rivers. The number of oysters in the Bay is currently at 1% of its historic level [2].

II.STAKEHOLDER ANALYSIS

A. West/Rhode Riverkeeper Inc.West/Rhode Riverkeeper Inc. is a non-profit organization

established in 2005 with the purpose to stop pollution, enforce environmental laws, and promote restoration in the West and Rhode rivers. The organization is funded through grants and the community through fundraisers and donations, and currently consists of one full-time Riverkeeper, two part-time staff, and several volunteers. The W/R Riverkeeper is also a licensed member of the Waterkeeper Alliance, an international group of Waterkeeper organizations. In addition, the Riverkeeper also works in collaboration with fifteen other Riverkeeper organizations within the Chesapeake Bay area and its tributaries. The objective of the Riverkeeper organization is to work with state and local governments in order to accomplish its goal of a clean waterway for the community.

B. Maryland WatermenThe local Maryland Watermen are citizens who make a

living from fishing/harvesting fish, crab, and oysters from the Chesapeake Bay and its tributaries. Once a prosperous industry, currently Maryland has seen a decline in working watermen due to overharvesting and environmental changes. As excess nutrients and sediment are runoff into the

Figure 1 – Secchi Depth of West/Rhode River(1984 – 2011)

Aquaculture System for the West and Rhode RiversAmy Crockett, Amir Delsouz, John DeGregorio, Alan Muhealden, Daniel Streicher

Chesapeake Bay, many aquatic species have been affected by the ecological decline in sub aquatic vegetation. This has resulted in near-historic lows of blue crab populations, as well as declining eastern oyster populations. In response to this change, watermen require new methods to continue earning an income from the Chesapeake Bay. One of these methods would be to implement an oyster aquaculture program as compared to harvesting oysters from the natural population. This would provide a sustainable source of product in order to offset the current condition of aquatic populations in the West and Rhode river. The objective of the Watermen is to provide an income to sustain their living through the harvest and sale of aquatic species, a business that is currently in danger of being unprofitable.

C. Maryland Department of Natural ResourcesThe Maryland Department of Natural Resources

(MDDNR) is the governing body of the Chesapeake Bay and its tributaries, responsible for managing the coastal regions as well. In addition to regulating the use of the waters, the MDDNR also promotes and supports the aquaculture enterprise. Through providing leases and loans for local watermen, the MDDNR plays an active role in sustaining the profitability of aquatic harvesting in Maryland. The objective of the MDDNR is to provide regulation of the Chesapeake waterways, as well as support the aquaculture industry.

D. Watershed ResidentsThe residents surrounding the West and Rhode river

support the restoration and protection of the water, although they also contribute excess runoff through yard and storm water drainage. Construction sites, fuel stations, and boating communities also contribute to this nutrient runoff and sediment erosion. With the creation of the West/Rhode Riverkeeper, these negative impacts have been measured and solutions to reducing environmental impact have been publicized over the past decade. The objective of residents is to support the recreational use of the rivers, as well as provide advocacy for a cleaner environment.

III. STATEMENT OF NEED

A system is needed to increase the Secchi depth of the West and Rhode Rivers to at least 1 meter that will also be financially sustaining, netting at least $36,000 per year in 5 years.

IV. DESIGN ALTERNATIVES

The alternatives considered in this study must be (1) commercially available and (2) legally allowed for use in the West/Rhode Rivers.

A. Obtaining the OysterThe lifecycle of an oyster starts when an egg and sperm combine to make a fertilized egg. After approximately one week, the oyster reaches the larvae stage; the first alternative of obtaining. If the oyster is obtained at this stage, it

continues to grow in a method called remote setting, in which multiple larvae attach itself to recycled full shell. After one more week, the larvae begins to grow a “foot.” It is at this stage that it called a seed; the second alternative of obtaining. If this alternative is chosen a growth method called nursery is required to grow the oyster. In this method, the one seed attaches itself to one finely crushed shell. Because of this, seed oysters grown using the nursery method are ideal when the final product desired is half shell. The seed uses this “foot” to attach itself to a shell. This stage, and third alternative of obtaining, is called spat-on-shell. Once this stage is reached, the spat-on-shell is ready to be placed into the water and in an aquaculture system. For the next 2-3 years, the oyster will grow, filtering water and growing its own shell, until it is large enough to be sold.

B. Final ProductThe most profitable oyster aquaculture system will have to take into consideration the final product that is desired based on the stage chosen to obtain the oyster. Each alternative of obtaining can use a growing method that produces a shucked or half shell final product. When a shucked oyster is desired as a final product, it allows the grower to reuse the shell for future use. Because shell cost is currently very high, being able to get it back would decrease equipment costs in the future and thereby increase total profit. Because the shell is shucked from the oyster, the oyster must be sold for canning purposes. On the other hand, if a half-shell oyster is desired as a final product, it can typically be sold for more as they are highly demanded by restaurants, but it is not possible to reuse the shell because it is included in the sale.

C. Selling MethodFor each alternative in stages 1 and 2 there are also two alternatives for selling the final product: direct and wholesale. Direct sale is where the seller must keep in contact with local restaurants and chefs, leading one-on-one demonstrations to help brand their company’s final product. This requires a large investment of time and energy by the seller. The other selling method, wholesale, which requires less of an investment of time and energy by the producer, involves selling the oysters in large quantities, which are then retailed by certified dealers [19].

V. METHOD OF ANALYSIS

The method of analysis includes evaluating the growth and survivability of the three alternatives for obtaining the oysters in the growth model, then evaluating the amount of nutrients filtered with the Two Dimensional Tidal Mixing Model (2DTMM) while evaluating the financial feasibility in the business model, next the design alternatives will be evaluated by the utility function, and finally the alternatives with be evaluated based on the cost benefit analysis.

A. Growth ModelOur approach to modeling the population of oysters is through a mass-balance approach. We’ll measure the amount of oyster biomass based on the organic carbon incorporated in soft tissue per unit area using equation (1). This will be computed using the oyster biometric variables; (IF) which is the fraction ingested (0 < IF < 1), (Fr) filtration rate (m^3 g^-1 oyster C d^-1), (RF) respiratory fraction, (BM) basal metabolic (d^-1), (α) assimilation efficiency (0 < α < 1), and (β) mortality rate (d^-1).

dOdt

=α∗Fr∗POC∗IF (1−RF)∗O−BM∗O−β∗O

For our model’s time (t) variable, we will be using tidal cycles in the 2DTMM. The tidal cycles will be subject to the environmental variables (T) temperature, (DO) dissolved oxygen, (S) salinity, (TSS) total suspended solids, and (POC) particulate organic carbon (g m^3). We are neglecting the disease variable due to the fact that all oysters are considered diseased, and although the diseased oysters have a reduced life span (from 30 years to 7 years) this will not affect our design since we will be harvesting oysters for profit at a maximum span of 3 years from spat [21]. On the issue of the height/depth phenomenon, or otherwise defined as stratification of the environmental variables, the population model will be assumed to have evenly mixed values throughout the total depth of the water column. This assumption is based on data taken while out on the West and Rhode River at two separate dates in order to avoid correlated data.

B. 2-D Tidal Mixing Model (2DTMM)A 2DTMM was designed to predict the amount ofnutrients and TSS removed from the WRR by the designalternatives, which act as sinks in the model. The continuous tide flow process is modeled in discrete time steps of 1.5 hours. This duration was selected because the 6-hour flood and ebb tides cross a series of 4 cells in each river, shown in Figure 3. Note that the transitions from cells 7-8 and 7-9 occur simultaneously. The state variables in the model are recalculated after each time step and at the end of each tide cycle; the state variables are stored and used in the next tide cycle iteration. The inputs and outputs of the2DTMM are shown in Figure 2, with N and P referring to nitrogen and phosphorus.

C. Business ModelThe growth model will input the number of oysters

available to be sold in a particular year. Then the revenue will be calculated based on the number of oysters available to be sold. The cost will go through a time decision node. If the time is less than five years, there will be an additional cost of a loan payment or other start-up costs. This will then

Figure 2 – Method of Analysis FlowchartTime (Days)

Oys

ter B

iom

ass (

g C)

Figure 3 – Notional Oyster Growth

Figure 4 – Business Model Flow Chart

be added to the other seasonal operation costs and then be subtracted from the revenue. If the time is more than five years the cost will only include the seasonal operation costs and then be subtracted from revenue. The reason for the five year time decision if because the loans offered by the state of Maryland are for five years. Once the cost is subtracted from the revenue there is another time decision node. If the time is less than three years, the decision to continue the business will be based on the number of oysters which survived the year. If the threshold number of oysters survived the year, the model will continue and the model will simulate another year. If the time is greater than or equal to three years, the continuation of the business will be based upon profit. If there was a profit made the model will continue for another year. The reason the decision to continue the model for an additional year is split into survivability and profit is based on the initial research that it will take oysters about three years to grow to a three inch size. The current legal restrictions on selling oysters regulate an oyster must be at least three inches to legally sell it. It typically takes oysters two to three years to reach this stage. It is unreasonable to base the decision to continue a business based on profit, if there is nothing to be sold until the third year. Based on the growth model, the number of years may be changed to reflect the first estimated time of selling oysters.

VI. RESULTS

These results are notional and have been estimated from arbitrary values. They are evaluating a series of combinations of design alternatives to determine which is the most profitable. The fluctuations represent the difference in growth and the number of oysters ready to be sold from one year to the next. The large drops represent years like the summer of 2011 when the salinity or another environmental variable drops to extreme conditions and the oyster growth is significantly affected.

VII. DISCUSSION AND RECOMMENDATIONS

The information here still needs to be evaluated, as well as cost vs. utility analysis.

ACKNOWLEDGMENT

The Aquaculture System team would like to give special acknowledgement to individuals who contributed to the completion of this project:

George L. Donohue, PhD and Chris Trumbauer and Joe Ports: representing West/Rhode Riverkeeper. Lance Sherry, PhD: GMU faculty advisor.

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Figure 5 – Notional Profit from Wholesale

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