Daniel E. Campbell

Emergy Analysis of Human Carrying Capacity and Regional Sustainability: An Example Using the State of Maine

The human carrying capacity for a region at a specified standard of living depends on the economic and environmental resources of the region and the exchange of resources across regional boundaries. The length of time that a human population living at a given standard can be sustained depends on the rates of use and renewal of the resource base. All environmental, economic, and social resources are produced as a result of energy transformations; therefore, the energy required for their production can be specified and evaluated in common terms by converting their energy values into emergy. Emergy is defined as the available energy of one kind, previously used up directly and indirectly to make a product or service. Its unit is the emjoule. Emergy values and indices are used to evaluate the resource base for Maine, a politically defined region, and to estimate its human carrying capacity at the 1980 standard of living and for possible future resource bases. Emergy indices for Maine are compared with similar indices for Florida, Texas, and the United States to demonstrate variations in human carrying capacity and sustainability among different regions. The 1980 standard of living for Maine, Florida, Texas, and the Nation as measured by emergy use per person fell within a relatively narrow range of 3.4E16 to 4.3E16 solar emjoules y-1. The human carrying capacity for a region is considered within a pulsing paradigm for sustainabilty and within the constraints provided by a renewable resource base. For example, in the short-term the developed human carrying capacity for Maine is largely determined by the fuel emergy inflow relative to renewable emergy resources. If purchased emergy inflows relative to Maine’s renewable emergy increase to the average ratio for a developed country around 1980, the population living in Maine at 1980 standards could increase to 2.9 million or 2.6 times Maine’s 1980 population. In contrast, the human carrying capacity based on Maine’s renewable resources alone was 0.37 million people at the 1980 standard of living or 33% of the 1980 population.

Developing and applying a benthic index of estuarine condition for the Virginian Biogeographic Province

A benthic index of estuarine condition was constructed for the Virginian Biogeographic Province (from Cape Cod, Massachusetts, to the mouth of Chesapeake Bay, Virginia) with data collected during summers of 1990 through 1993 by the US EPA’s Environmental Monitoring and Assessment Program (EMAP). Forty-eight metrics, based on attributes of the macrobenthos, were considered for the index, including measures of biodiversity, community condition, individual health, functional organization, and taxonomic composition. Salinity was correlated significantly with some of the metrics. Therefore, some metrics were normalized for salinity. The data used to develop the index (the calibration data) included equal numbers of reference and degraded sites, distributed equally across three salinity zones ( 18‰). An independent set of data was used for validation. Linear discriminant analysis identified combinations of metrics that could best discriminate reference from degraded sites. The targets for correct classification were 90% of the sites for the calibration data and 80% for the validation data. Six combinations of metrics were identified. The final index was based on the ecological interpretation and relevance of the individual metrics and the ability to meet the calibration and validation targets. The final index consisted of three metrics: a positive contribution from salinity-normalized Gleason’s D (a biodiversity metric), and negative contributions from two taxonomic composition metrics, abundances of spionid polychaetes and of salinity-normalized tubificid oligochaetes. The index correctly classified 87% of reference and 90% of degraded sites in the calibration data and 88% of reference and 81% of degraded sites in the validation data. The index correctly classified sites over the full range of salinity (tidal-fresh to marine waters) and across grain sizes (silt–clay to sand).

Development of the mussel aquaculture lease site model MUSMOD©: a field program to calibrate model formulations

Abstract Field observations were used along with mathematical modelling to develop model formulations to represent mussel (Mytilus edulis) growth at several shallow subtidal study sites along the Maine coast, USA. In order to match predicted growth from the model MUSMOD© (D.E. Campbell, C.R. Newell, 1997. MUSMOD©: A mussel production model for use on bottom culture lease sites. J. Exp. Mar. Biol. Ecol., in press.) with observed growth rates in the field, modifications were made in the model with respect to: (a) factors affecting the supply of food to the mussel feeding zone (vertical mixing, settling, resuspension and particle depletion); (b) short-term variability in mussel feeding and respiration over a tidal cycle; (c) the effects of seasonal variations in food quality on assimilation, scope for growth, and observed growth. Surface and bottom water samples taken from 1989 to 1991 revealed daily fluctuations in SPM, POM, chlorophyll a, particulate carbon and nitrogen, and phytoplankton carbon which were similar to annual ranges. Maine waters are typified by a spring diatom bloom, followed by a rise in detritus in early summer. Successful representation of mussel growth was obtained when food concentration was expressed as phytoplankton and detrital carbon, and assimilation was modelled as a function of food type (phytoplankton or detritus), and detritus quality (as percent of maximum annual N/C ratio of the detritus). By expressing particle depletion as a percent reduction from conditions at the edge of the lease site, scope for growth was modelled over an annual period. Observations with a time-lapse benthic video monitor (TLBVM) and flow-through physiological chambers demonstrated tidal variations in filtration rate, respiration rate and shell gape in subtidal mussels, with periods of valve closure correlated with low particle concentrations. These observations support the hypothesis that mussel energy gain is maximized during fluctuating food availability by the control of pumping rate via the shell gape response. This may explain why field observations of filtration rate are sometimes lower than maximum published values, and allows the mussels to maintain a slightly positive scope for growth by reducing respiratory losses when food particles are limiting. The settling flux of phytoplankton and detritus, while poorly characterized in coastal New England waters, provides over 30% of the estimated food supply to subtidal mussel cultures and may explain, in part, the patterns of shell gape observed in this study.

MUSMOD©, a production model for bottom culture of the blue mussel, Mytilus edulis L.

Abstract A mussel production model, MUSMOD© was developed to seed bottom culture lease sites in Maine to their carrying capacity. The process of model development is demonstrated with three models: (a) an initial conceptual model, (b) an aggregated model driven by the tidal exchange of food particles and (c) MUSMOD©, the final model driven by food supplied in the tidal flow of water across a site. The final model predicts mussel production using the concentrations of phytoplankton and detritus in the surface water, detritus quality, tidal current speed, water depth and temperature. Field measurements of several quantities (e.g., clearance, respiration, growth rates for shell and meat, food concentration gradient, and temporal feeding pattern, (Newell et al., 1997, Development of the mussel aquaculture lease site model, MUSMOD©: a field program to calibrate model formulations, J. Exp. Mar. Biol. Ecol., this volume) were obtained to evaluate and calibrate the final model. Model refinement using iterations of modeling and field work demonstrated the importance of food quantity and quality in explaining the observed patterns of mussel growth. Food quantity explained the first-order growth pattern, but it was necessary to account for the quality of the food to explain the second-order details of growth. Vertical mixing supplied the majority of new food particles, however, particles settling over the mussel bed during slack water accounted for 33% of the phytoplankton and 45% of the detritus entering the feeding layer from above. A sensitivity analysis of the effects of seed density on mussel growth using MUSMOD© identified the optimum carrying capacity for three Maine lease sites. Seeding mussels during the optimum time period (May to early July) resulted in the harvest of marketable mussels from 40 mm seed in 8 months for a high food year and in 13 months when the food supply was low. Characterizing the food supply using particulate organic matter, POM, alone was not sufficient to explain mussel growth in the detail necessary to answer many farm management questions.

Evaluation and Emergy Analysis of the Cobscook Bay Ecosystem

Abstract A naturally eutrophic, estuarine ecosystem with many unique features has developed in Cobscook Bay over the past four thousand years under the influence of six meter tides and rich flows of nitrogen from the deep waters of the Gulf of Maine. In this paper, measurements of primary production and water column properties made in the Bay from 1995 to 1996 and information from past studies are used to construct an energy systems model of the Bays ecosystem and to evaluate the annual flows of energy and matter coursing through this network. The properties of this ecosystem network were analyzed in terms of the solar emjoules (emergy) required to support primary and secondary production. In Cobscook Bay there is an extraordinary convergence of emergy, 7.4E+12 sej m −2, from renewable sources. This level of emergy is one of the highest natural empower densities that we have found. Eighty-four percent of this emergy is from the tides and wave action. Transformities calculated in this analysis show that emergy is being used, most effectively, to support populations of large brown alga, i.e., Ascophyllum nodosum, Fucus vesiculosus, and Laminaria longicruris, and the diverse community of benthic organisms that thrive in the intertidal and shallow subtidal zone along the shore. Phytoplankton production is less efficient apparently due to light limitation, but phytoplankton and resuspended benthic microalgae support highly productive beds of filter feeders. Empower density in Cobscook Bay is similar to that required elsewhere for intensive fish culture; therefore, aquaculture may be a good human use of the rich convergence of natural emergy found there. The nitrogen entering Cobscook Bay from salmon culture is 19% of the net annual flux of new nitrogen entering from the coastal waters. The Bays great resource wealth supports economic activities such as salmon culture and commercial dragging for scallops and urchins that, in turn, alter the concentrations of nutrients and suspended sediments locally in the Bay and may cause increased sedimentation and changing benthic communities in the Bay as a whole.

Ecological and economic dynamics of the Shunde agricultural system under China's small city development strategy

The agricultural and industrial development of small cities is the primary environmental management strategy employed to make full use of extra labor in the rural areas of China. The ecological and economic consequences of this development strategy will affect over 100 million people and change the organization of the Chinese landscape. In this study, we examined the agricultural development of Shunde, a small city in Guangdong Province, over the period 1978 until 2000. Our analysis of the ecological and economic dynamics of the agricultural system revealed the dominant role of labor in the intensification of agricultural production, even though the use of fuels, fertilizers and machines also increased during this time. The Shunde agricultural system was examined from both biophysical or donor-based and human utility or receiver-based perspectives, using emergy and economic methods, respectively. After 22 years of urbanization, the Shunde agricultural system was still able to fill 96% of the local demand for agricultural products using only 6% of its total yield compared to using 14% of the total yield in 1978. Aquaculture developed quickly during the study period as grain production decreased. In 2000, the production of fish, pork, and vegetables accounted for 92% of the total emergy output of the system; however, the emergy buying power of the money received in exchange was lower than the emergy contained in the products exported. The excess emergy exported is the basis for a high quality diet delivered to city dwellers at a relatively low price. In the 1980s, the productivity of both land and labor increased; but after 1992 the productivity of labor decreased, causing the efficiency of the whole agricultural system to decrease. We recommend that processing plants be established for the main agricultural products of Shunde to decrease the emergy loss in trading and to increase employment. The effect of including monetized ecosystem services in the balance between the emergy delivered to the markets in agricultural products and the emergy buying power of the money received was to decrease the emergy gained by the Shunde agricultural system.

Development of a multidisciplinary approach to assess regional sustainability

There are a number of established, scientifically supported metrics of sustainability. Many of the metrics are data-intensive and require extensive effort to collect data and compute the metrics. Moreover, individual metrics do not capture all aspects of a system that are relevant to sustainability. A pilot project was initiated to create an approach to measure, monitor, and maintain prosperity and environmental quality of a regional system. The goal was to produce a straightforward, inexpensive methodology that is simple to use and interpret. This requires historical data be readily accessible, metrics must be applicable to the relevant scale, and results must meet the needs of decision-makers. Because sustainability is a multidimensional concept, the research group consisted of a multidisciplinary team that identified the major components of an environmental system. We selected metrics to capture the multidimensionality of sustainability in environmental systems and included: (1) emergy to capture the quality-normalized flow of energy through the system; (2) ecological footprint to capture the impact of humans on the system; (3) green net regional product to estimate human prosperity and well being within the system; and (4) Fisher information to capture the dynamic order of the system. We were able to compute metrics for a test geographic region using existing datasets. Preliminary analysis indicates that each metric reveals a somewhat different trend. These preliminary findings support the idea that characterization of sustainability requires a multidisciplinary approach and demonstrate the need to measure multiple aspects of an environmental system.

Can sediment total organic carbon and grain size be used to diagnose organic enrichment in estuaries

Eutrophication (i.e., nutrient enrichment, organic enrichment, and oxygen depletion) is one of the most common sources of impairment in Clean Water Act 303(d)-listed waters in the United States. Although eutrophication can eventually cause adverse effects to the benthos, it may be difficult to diagnose. Sediment organic carbon (OC) content has been used as an indicator of enrichment in sediments, but the amount of surface area available for carbon adsorption must be considered. We investigated the utility of the relationship between OC and sediment grain size as an indicator of eutrophication. Data from the U.S. Environmental Protection Agencys Environmental Monitoring and Assessment Program was used to test this relationship. However, anthropogenic contaminants are also capable of causing adverse effects to the benthos and often co-occur with elevated levels of OC. Contaminant analysis and toxicity tests were not consistently related to enrichment status as defined by relationship between total OC and grain size. Although variability in response occurred, reflecting the variance in the water column factors (dissolved oxygen, chlorophyll a, and nutrients) and limited sample sizes, the data supported the hypothesis that sites designated as enriched were eutrophied. Dissolved oxygen levels were reduced at enriched sites, whereas chlorophyll a and nutrients were higher at enriched sites. This suggests that the relationship of OC to grain size can be used as a screening tool to diagnose eutrophication.

Relationships among the Energy, Emergy, and Money Flows of the United States from 1900 to 2011

Energy Systems Language models of the resource base for the U.S. economy and of economic exchange were used, respectively, (1) to show how energy consumption and emergy use contribute to real and nominal GDP and (2) to propose a model of coupled flows that explains high correlations of these inputs with measures of market-based economic activity. We examined a 3rd power law model of growth supported by excess resources and found evidence that it has governed U.S. economic growth since 1900, i.e., nominal GDP was best explained by a power function of total emergy use with exponent 2.8. We used a weight of evidence approach to identify relationships among emergy, energy, and money flows in the U.S. from 1900 to 2011. All measures of quality adjusted energy consumption had a relationship with nominal GDP that was best described by a hyperbolic function plus a constant and the relationship between all measures of energy consumption and real GDP was best described by a 2nd order polynomial. The fact that energy consumption per unit of real GDP declined after 1996 as real GDP continued to increase indicates that energy conservation or a shift toward less energy intensive industries has resulted in lower fossil fuel use and reduced CO2 emissions, while maintaining growth in real GDP. Since all energy consumption measures vs. real GDP deviated from a power law relationship after 1996; whereas, total emergy use did not, we concluded that total emergy use captured more of the factors responsible for the increase in real GDP than did energy measures alone, and as a result, total emergy use may be the best measure to quantify the biophysical basis for social and economic activity in the information age. The Emergy to Money Ratio measured as solar emjoules per nominal

Ecosystem Health: Energy Indicators

followed a decreasing trend from a high of 1.01E+14 semj/