Joanna K. York

Bio: Joanna K. York is an academic researcher from University of Delaware. The author has contributed to research in topics: Estuary & Nitrate. The author has an hindex of 8, co-authored 13 publications receiving 1691 citations. Previous affiliations of Joanna K. York include Virginia Tech & Marine Biological Laboratory.

Mangrove forests: one of the world's threatened major tropical environments.

Abstract: he mass media and scientific press have widely reported losses of tropical environments, such as fellingof rain forests and bleaching of coral reefs.This well-meritedattention has created a worldwide constituency that supportsconservation and restoration efforts in both of these threat-ened ecosystems. The remarkable degree of public aware-ness and support has been manifested in benefit rock concertsat Carnegie Hall and in the designation of ice cream flavorsafter rain forest products. Mangrove forests are another im-portant tropical environment,but these have received muchless publicity.Concern about the magnitude of losses of man-grove forests has been voiced mainly in the specialized liter-ature (Saenger et al. 1983, Spalding et al. 1997).Mangrove trees grow ubiquitously as a relatively narrowfringe between land and sea, between latitudes 25°N and30°S.They form forests of salt-tolerant species,with complexfood webs and ecosystem dynamics (Macnae 1968,Lugo andSnedaker 1974, Tomlinson 1986).Destruction of mangrove forests is occurring globally.Global changes such as an increased sea level may affect man-groves (Ellison 1993,Field 1995),although accretion rates inmangrove forests may be large enough to compensate for thepresent-day rise in sea level (Field 1995).More important,itis human alterations created by conversion of mangroves tomariculture,agriculture,and urbanization,as well as forestryuses and the effects of warfare, that have led to the remark-able recent losses of mangrove habitats (Saenger et al. 1983,Fortes 1988, Marshall 1994, Primavera 1995, Twilley 1998).New data on the magnitude of mangrove area and changesin it have become more readily available, especially with theadvent of satellite imagery and the Internet. Moreover, in-formation about the function of mangrove swamps, theirimportance in the sustainability of the coastal zone, and theeffects of human uses of mangrove forests is growing. Somepublished regional assessments have viewed anthropogenicthreats to mangrove forests with alarm (Ong 1982,Fortes 1988,Ellison and Farnsworth 1996),but reviews at the global scaleare dated (Linden and Jernelov 1980, Saenger et al. 1983).We collated and revised published information to reviewthe status of mangrove swamps worldwide.To assess the sta-tus of this major coastal environment, we compiled and ex-amined available data to quantify the extent of mangroveforest areas in different parts of the world,the losses of man-grove forest area recorded during recent decades, and therelative contributions by various human activities to theselosses.We first assessed current mangrove forest area in tropicalcountries of the world.It is difficult to judge the quality of thesedata in the published literature, because in many cases themethods used to obtain them were insufficiently described andthe associated uncertainty was not indicated. Much infor-mation based on satellite imagery is summarized in the

Stable isotopic detection of ammonium and nitrate assimilation by phytoplankton in the Waquoit Bay estuarine system

Abstract: We measured concentration and d15N of chlorophyll a (Chl a), NO 2 , and NH þ along a salinity gradient in Childs River, Massachusetts, in winter, spring, and summer. We used the d15N of Chl a as a proxy for the phytoplankton d15N to minimize potential ambiguities from other material in seston. NO 2 concentration ranged from 0 to 50 mmol L21 and NH þ from 0 to 8 mmol L21; both forms decreased with increasing salinity. NO 2 concentration was generally higher than NH þ . Chl a concentrations ranged between 1 and 15 mg m23 in winterspring and had a summer midestuarine peak of 95 mg m23. The d15 No f NO 2 and NH þ ranged from –10% to +7% and –3% to +13%, respectively, and decreased approximately linearly with increasing salinity. The d15 No f NO 2 reflected the predominance of groundwater as the source of NO 2 to the estuary, whereas the d 15 No f NH þ indicated that regeneration was the main NH þ source. Throughout the estuary, NO 2 was isotopically lighter than NH þ . Phytoplankton d15N increased from winter to summer and was relatively invariant with salinity, in contrast to the d15N of dissolved inorganic nitrogen. A comparison of the d15N of phytoplankton, NO 2 , and NH þ indicated that phytoplankton in Childs River derived 53% to 97% of their N from NH þ . Phytoplankton acquired their stable nitrogen isotopic ratio upstream, then maintained that ratio during downstream transport. The fractionation factor for phytoplankton NH þ uptake was +4.0% 6 0.6%, which was in the lower range of other estimates, indicating that phytoplankton might have been N limited.

Nitrogen Loads to Estuaries from Waste Water Plumes: Modeling and Isotopic Approaches

Abstract: We developed, and applied in two sites, novel methods to measure ground water-borne nitrogen loads to receiving estuaries from plumes resulting from land disposal of waste water treatment plant (WWTP) effluent. In addition, we quantified nitrogen losses from WWTP effluent during transport through watersheds. WWTP load to receiving water was estimated as the difference between total measured ground water-transported nitrogen load and modeled load from major nitrogen sources other than the WWTP. To test estimated WWTP loads, we applied two additional methods. First, we quantified total annual waste water nitrogen load from watersheds based on nitrogen stable isotopic signatures of primary producers in receiving water. Second, we used published data on ground water nitrogen concentrations in an array of wells to estimate dimensions of the plume and quantify the annual mass of nitrogen transported within the plume. Loss of nitrogen during transport through the watershed was estimated as the difference between the annual mass of nitrogen applied to watersheds as treatment plant effluent and the estimated nitrogen load reaching receiving water. In one plume, we corroborated our estimated nitrogen loss in watersheds using data from multiple-level sampling wells to calculate the loss of nitrogen relative to a conservative tracer. The results suggest that nitrogen from the plumes is discharging to the estuaries but that substantial nitrogen loss occurs during transport through the watersheds. The measured vs. modeled and stable isotopic approaches, in comparison to the plume mapping approach, may more reliably quantify ground water-transported WWTP loads to estuaries.

Trophic Links in the Plankton in the Low Salinity Zone of a Large Temperate Estuary: Top-down Effects of Introduced Copepods

Abstract: We investigated trophic relationships involving microzooplankton in the low salinity zone of the San Francisco Estuary (SFE) as part of a larger effort aimed at understanding the dynamics of the food web supporting the endangered delta smelt, Hypomesus transpacificus. We performed 14 cascade experiments in which we manipulated the biomass of a copepod (Limnoithona tetraspina, Pseudodiaptomus forbesi, or Acartiella sinensis) and quantified responses of lower trophic levels including bacterioplankton, phytoplankton, and microzooplankton. Microzooplankton comprised a major food source for copepods; 9 out of 14 experiments showed removal of at least one group of microzooplankton by copepods. In contrast, the impact of copepods on phytoplankton was indirect; increased copepod biomass led to greater growth of phytoplankton in 3 of 14 experiments. Estimated clearance rates on microzooplankton were 4 mL day−1 for L. tetraspina and 2–6 mL day−1 for P. forbesi, whereas A. sinensis consumed mainly copepod nauplii. Complex trophic interactions, including omnivory, among copepods, microzooplankton, and different components of the phytoplankton likely obscured clear trends. The food web of the SFE is probably less efficient than previously thought, providing poor support to higher trophic levels; this inefficient food web is almost certainly implicated in the continuing low abundance of fishes, including the delta smelt that use the low salinity zone of the San Francisco Estuary.

Microzooplankton Grazing in Green Water—Results from Two Contrasting Estuaries

Abstract: We measured seasonal variations in microzooplankton grazing in Long Island Sound (LIS) and San Francisco Bay (SFB). There was consistent evidence of nutrient limitation in LIS, but not SFB. We found higher chlorophyll a concentrations in LIS compared with SFB. In spite of differences in phytoplankton, there were no differences in microzooplankton abundance (summer: LIS, 12.4 ± 1.8 × 103 indiv. L−1; SFB, 14.1 ± 3.0 × 103 indiv. L−1), biomass (summer: LIS, 30.4 ± 5.0 μg C L−1; SFB, 26.3 ± 5.9 μg C L−1), or grazing rates (summer: LIS, 0.66 ± 0.19 day−1; SFB, 0.65 ± 0.18 day−1) between the two estuaries. In common with many other investigators, we found many instances of saturated as well as insignificant grazing. We suggest that saturation in some cases may result from high particle loads in turbid estuarine systems and that insignificant grazing may result from extreme saturation of the grazing response due to the need to process non-food particles.

The value of estuarine and coastal ecosystem services

Abstract: The global decline in estuarine and coastal ecosystems (ECEs) is affecting a number of critical benefits, or ecosystem services. We review the main ecological services across a variety of ECEs, including marshes, mangroves, nearshore coral reefs, seagrass beds, and sand beaches and dunes. Where possible, we indicate estimates of the key economic values arising from these services, and discuss how the natural variability of ECEs impacts their benefits, the synergistic relationships of ECEs across seascapes, and management implications. Although reliable valuation estimates are beginning to emerge for the key services of some ECEs, such as coral reefs, salt marshes, and mangroves, many of the important benefits of seagrass beds and sand dunes and beaches have not been assessed properly. Even for coral reefs, marshes, and mangroves, important ecological services have yet to be valued reliably, such as cross-ecosystem nutrient transfer (coral reefs), erosion control (marshes), and pollution control (mangroves). An important issue for valuing certain ECE services, such as coastal protection and habitat-fishery linkages, is that the ecological functions underlying these services vary spatially and temporally. Allowing for the connectivity between ECE habitats also may have important implications for assessing the ecological functions underlying key ecosystems services, such coastal protection, control of erosion, and habitat-fishery linkages. Finally, we conclude by suggesting an action plan for protecting and/or enhancing the immediate and longer-term values of ECE services. Because the connectivity of ECEs across land-sea gradients also influences the provision of certain ecosystem services, management of the entire seascape will be necessary to preserve such synergistic effects. Other key elements of an action plan include further ecological and economic collaborative research on valuing ECE services, improving institutional and legal frameworks for management, controlling and regulating destructive economic activities, and developing ecological restoration options.

Accelerating loss of seagrasses across the globe threatens coastal ecosystems

Abstract: Coastal ecosystems and the services they provide are adversely affected by a wide variety of human activities. In particular, seagrass meadows are negatively affected by impacts accruing from the billion or more people who live within 50 km of them. Seagrass meadows provide important ecosystem services, including an estimated $1.9 trillion per year in the form of nutrient cycling; an order of magnitude enhancement of coral reef fish productivity; a habitat for thousands of fish, bird, and invertebrate species; and a major food source for endangered dugong, manatee, and green turtle. Although individual impacts from coastal development, degraded water quality, and climate change have been documented, there has been no quantitative global assessment of seagrass loss until now. Our comprehensive global assessment of 215 studies found that seagrasses have been disappearing at a rate of 110 km(2) yr(-1) since 1980 and that 29% of the known areal extent has disappeared since seagrass areas were initially recorded in 1879. Furthermore, rates of decline have accelerated from a median of 0.9% yr(-1) before 1940 to 7% yr(-1) since 1990. Seagrass loss rates are comparable to those reported for mangroves, coral reefs, and tropical rainforests and place seagrass meadows among the most threatened ecosystems on earth.

A blueprint for blue carbon: toward an improved understanding of the role of vegetated coastal habitats in sequestering CO2

Abstract: Recent research has highlighted the valuable role that coastal and marine ecosystems play in sequestering carbon dioxide (CO(2)). The carbon (C) sequestered in vegetated coastal ecosystems, specifically mangrove forests, seagrass beds, and salt marshes, has been termed blue carbon. Although their global area is one to two orders of magnitude smaller than that of terrestrial forests, the contribution of vegetated coastal habitats per unit area to long-term C sequestration is much greater, in part because of their efficiency in trapping suspended matter and associated organic C during tidal inundation. Despite the value of mangrove forests, seagrass beds, and salt marshes in sequestering C, and the other goods and services they provide, these systems are being lost at critical rates and action is urgently needed to prevent further degradation and loss. Recognition of the C sequestration value of vegetated coastal ecosystems provides a strong argument for their protection and restoration; however, it is necessary to improve scientific understanding of the underlying mechanisms that control C sequestration in these ecosystems. Here, we identify key areas of uncertainty and specific actions needed to address them.

Mangrove forests: Resilience, protection from tsunamis, and responses to global climate change

Abstract: This review assesses the degree of resilience of mangrove forests to large, infrequent disturbance (tsunamis) and their role in coastal protection, and to chronic disturbance events (climate change) and the future of mangroves in the face of global change. From a geological perspective, mangroves come and go at considerable speed with the current distribution of forests a legacy of the Holocene, having undergone almost chronic disturbance as a result of fluctuations in sea-level. Mangroves have demonstrated considerable resilience over timescales commensurate with shoreline evolution. This notion is supported by evidence that soil accretion rates in mangrove forests are currently keeping pace with mean sea-level rise. Further support for their resilience comes from patterns of recovery from natural disturbances (storms, hurricanes) which coupled with key life history traits, suggest pioneer-phase characteristics. Stand composition and forest structure are the result of a complex interplay of physiological tolerances and competitive interactions leading to a mosaic of interrupted or arrested succession sequences, in response to physical/chemical gradients and landform changes. The extent to which some or all of these factors come into play depends on the frequency, intensity, size, and duration of the disturbance. Mangroves may in certain circumstances offer limited protection from tsunamis; some models using realistic forest variables suggest significant reduction in tsunami wave flow pressure for forests at least 100 m in width. The magnitude of energy absorption strongly depends on tree density, stem and root diameter, shore slope, bathymetry, spectral characteristics of incident waves, and tidal stage upon entering the forest. The ultimate disturbance, climate change, may lead to a maximum global loss of 10–15% of mangrove forest, but must be considered of secondary importance compared with current average annual rates of 1–2% deforestation. A large reservoir of below-ground nutrients, rapid rates of nutrient flux and microbial decomposition, complex and highly efficient biotic controls, self-design and redundancy of keystone species, and numerous feedbacks, all contribute to mangrove resilience to various types of disturbance.

A World Without Mangroves

Abstract: At a meeting of world mangrove experts held last year in Australia, it was unanimously agreed that we face the prospect of a world deprived of the services offered by mangrove ecosystems, perhaps within the next 100 years Mangrove forests once covered more than 200,000 km2 of sheltered tropical