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SCOR/LOICZ Working Group 112

"MAGNITUDE OF SUBMARINE GROUNDWATER DISCHARGE AND ITS INFLUENCE ON COASTAL OCEANOGRAPHIC PROCESSES"

Co-chairs: William C. Burnett and Evgeny A. Kontar

Sponsored by
the Scientific Committee on Oceanic Research (SCOR) 

and 

the Land-Ocean Interactions in the Coastal Zone (LOICZ) 
programme element of the 
International Geosphere-Biosphere Programme (IGBP)

Table of Contents: 

1. Objectives and Terms of Reference
2. Members, Associate Members, Participating Scientists
3. Organizational Structure and Work Plan
4. Summary
5. Scientific Background and Issues
6. Bibliography
7. News Article on WG-112

Organizational Structure and Work Plan

The following goals, approach, and potential deliverables were developed during an organizational meeting held in conjunction with the recent Western Pacific Geophysical Meeting in Taipei (July 21-24, 1998). The Working Group has identified three components to be addressed in meeting its overall objectives:

Overall Goal:
To define more accurately and completely how submarine groundwater discharge (SGD) influences chemical and biological processes in the coastal ocean. We will review and assess deficiencies in our knowledge concerning the magnitude of SGD fluxes in the coastal zone. This will include such aspects as a comparison of SGD to river flow, amount of fresh versus recycled seawater flow, measurement and modeling approaches, nutrient fluxes, input of pollutants, influence on coastal marine processes, etc.

Specific Goals:

1. Review and evaluate existing methods for assessment of SGD via modeling approaches. Identify needs and improvements in the field.
2. Define the existing methods and tools useful for direct measurement of groundwater fluxes to the coastal zone.
3. Develop and refine a typological approach to assess SGD over broad areas. These activities will include selection of appropriate parameters, identification of type areas, recommendation of necessary studies for proper evaluation, extrapolation to other areas; and a direct tie-in to the LOICZ typology data set.

In order to address these specific areas, three tasks have been defined, with responsibility for coordination of each task assigned to one WG member. The respective task coordinators will contact the appropriate working group members for suggestions and assignments.

Task 1: Calculation and Modeling

Coordinator:
Prof. Igor S. Zektser
Water Problems Institute
Russian Academy of Sciences
P.O. Box 231, 10 Novaya Basmannaya Str.
Moscow, 107078, RUSSIA
tel: (+7) (095) 265-9534
fax: (+7) (095) 265-1887
e-mail: zektser@iwapr.msk.su

1998-99 Activities and Objectives:
The main objectives of the "Calculation and Modeling" task is to evaluate the existing methods for estimating the magnitude of SGD into the coastal zone via modeling approaches. Deficiencies of these current methods will be reviewed and suggestions made for improvement. Close coordination with Tasks #2 and #3 will be particularly important as modeling will necessarily be the principal approach for large-scale assessment.

The task will perform these activities during the 1998-99 period:

1. A review of the modeling approaches used for regional to global scale assessments of SGD. The review will note the deficiencies and data needs for such assessments.
2. A compilation of data for regional scale assessment of SGD versus river flow for areas where sufficient information exists.
3. Compiling a set of recommendations on how the methodology for modeling approaches for estimating the magnitude of SGD flow and associated solute transport may be improved.

Task 2: Measurement, Sampling, and Experimental Design

Coordinator:
Dr. Makoto Taniguchi
Department of Earth Sciences
Nara University of Education
Nara 630-8528, JAPAN
tel (+81) 742-27-9202
fax: (+81) 742-27-9291
e-mail: makoto@nara-edu.ac.jp

1998-1999 Activities and Objectives:
The overall goal of this task is to evaluate the existing tools and methods for direct measurement of SGD in the coastal zone. We will review the methods currently in use, identify potential problems, and recommend solutions. Specifically, we plan to investigate the feasibility of organizing an intercalibration exercise for different designs of seepage meters. Such an intercomparison could also be extended to include other forms of measurement (e.g., natural and artificial tracers) and modeling as well. Identification of "flagship" field sites would be an important element of such an approach.

In order for such an exercise to be useful, careful selection of the study sites is essential. We will thus first review and consider the most important characteristics for such sites. One possibility is to search for areas with significantly different ratios of the groundwater recharge rate (GR) to specific runoff (SF), i.e., the river discharge per unit drainage area. Logistical and other considerations will have to be considered as well.

During the 1998-99 period, the following activities will be undertaken by the "Measurement, Sampling, and Experimental Design" task of WG-112:

1. A review of the various SGD measurements which have been applied with an assessment of the advantages and disadvantages of each.
2. Compilation of available data sets and a list of active researchers in this field.
3. Identification of the most desirable characteristics for intercalibration field sites and a short list of potential candidates.

Task 3: Typology, Integration and Globalization

Coordinator:
Dr. Robert W. Buddemeier
Kansas Geological Survey
University of Kansas
1930 Constant Ave.
Lawrence, Kansas 66047-3726 USA
tel: (+1) 785-864-3965
fax: (+1) 785-864-5317
e-mail: buddrw@kgs.ukans.edu

1998-99 Activities and Objectives:
The overall goal of the "Typology, Integration, and Globalization" task is to develop a classification system for coastal environments based on the probable magnitude, quality, and biogeochemical or oceanographic importance of SGD. In the WG-112 context this is expected to lead to refinement of process understanding and scientific questions, and to the identification of problems and opportunities for research. The larger LOICZ goals are to identify and quantify the role of the coastal zone in the biogeochemical processes of the total earth system; in this context, SGD typologies will be integrated with other coastal zone typology and budget developments.

During the 1998-1999 period, the following activities will be undertaken:

1. Convening, under LOICZ auspices, a coastal typology workshop with a strong orientation toward SGD issues;
2. Submission of advice and specifications of needs to other IGBP program elements and activities that may address issues relevant to SGD and typology;
3. Continued efforts to identify and disseminate information about relevant activities, researchers, or available data sets; and,
4. Development, first for WWW dissemination and ultimately for publication, of explanations and examples of the typology-budget approach to SGD and general coastal zone issues.

To the maximum extent possible, information will be posted and made available via the Web. Prior to the next meeting of WG-112, an informal written report will be circulated to members and other interested parties, outlining progress and identifying issues for future discussion or development.

The terrestrial portion of the coastal zone is an area of high human activity (agricultural, urban and industrial), with attendant perturbations and high gradients in water and contaminant fluxes. The problems of pathway identification and flux measurement discussed above become more critical at local scales; often aquifer characteristics and chemical sources are not well understood, and even where they are, there may not be adequate measurement points or data-local authorities and researchers tend to focus on the best resource or the worst problem, rather than the widely distributed marginal-quality water that may carry most of the chemical load or system-relevant "signal." This is illustrated in Figure 4 by the chemical inhomogeneity of the shallow aquifer. Where salinity increases and surface contamination decreases with depth, darcian flow estimates based on a limited number of measuring points may be highly misleading. Additionally, there may be problems of estimating consumptive water use (and therefore effective gradient or flux) between the sea and the lowest inland measuring point (monitoring well or gauging station).

Requirements for Integration and Application of Data

It is not realistic to expect that all measurements, calculations or publications of data relevant to coastal groundwater fluxes will suddenly conform to the needs (Gordon et al., 1995; Gordon et al., 1996) or standards (Boudreau et al., 1996) of the LOICZ project. However, one of the reasons for highlighting the disciplinary diversity in the origins and applications of the data is to encourage researchers both to seek out and to provide the data that will make their results more broadly useful-and in doing so, to encourage integration of the field of study.

In publishing, compiling, or databasing groundwater flux results, a wide variety of information should be considered, included, or referenced. Examples include geographic coordinates of drainage basins or aquifer units, coastline segments, and well or study sites. as well as information on the sources of both water level and groundwater chemistry data. The groundwater data should include land and water level (or head) elevations, relevant times of measurement, and depth or elevation of the screened (sampled) interval. Measured or assumed hydrogeologic parameters and stratigraphic aquifer characteristics are also required for interpretation-which means that information on methods of measurement or derivation is needed.

The challenge of effectively integrating and comparing diverse hydrologic and oceanographic measurements and models, often at very different spatial and temporal scales, demands extensive documentation of both primary data and methods, as well as rigorous analysis of uncertainties. The difference between semiquantitative groundwater flux estimates and determinations useful for flux budgets will be very great in terms of the quality of documentation and analysis required. At least as important, however, is the fact that estimates can be quite useful-if the assumptions, methods, and uncertainties are specified. Without this evaluation, estimates produced for one application may be seriously misleading if used for others.

Summary

Measurements or estimates of groundwater and associated chemical fluxes, especially over substantial areas or time periods, are notoriously uncertain. "Groundwater discharge" may include the base flow component of stream and river discharge, direct seepage from phreatic aquifers though the intertidal and shallow subtidal zones into the coastal ocean, nearshore springs, deeper offshore discharge (as from confined aquifers), or any combination of these. Depending on the measurements made and definitions used, combining groundwater flux estimates with independent estimates of fluvial inputs and oceanic fluxes can result in over- or under-estimates (for example, double-counting river base flow as both river input and groundwater flux, or failure to account for riverine groundwater discharge between the lowest gauging station and the mouth). Additional complications arise when one considers issues such as short-term interactions between streams and alluvial aquifers, or lateral "interflow" of water within the normally unsaturated zone-processes that may be hydrologically, but not biogeochemically, insignificant.

Hydrologic calculations may overestimate fluxes by neglecting evapotranspiration losses in the coastal plain. Vertical stratification of both flow rates and water quality in coastal aquifers can lead to serious mismatches in calculation of chemical fluxes, as can ocean water intrusion into the aquifer. Assignment of chemical compositions to the hydrologic fluxes requires careful matching of data sets, and consideration of the correspondence between the two types of data, their sources, and their uncertainties.

Complete reporting of data and methods, and consideration of the wide range of potential applications for data relating to groundwater in the coastal zone are recommended. This will not only serve the needs of integrative projects such as LOICZ, but will also provide definition and cohesiveness to an important field of study that is now highly fragmented.

References

Boudreau, P. R., P. J. F. Geerders, et al. (1996). LOICZ Data and Information System Plan. LOICZ Reports & Studies No. 6. Texel, The Netherlands., LOICZ: ii + 62.

Gordon, J., D. C. , P. R. Boudreau, et al. (1995). LOICZ Biogeochemical Modelling Guidelines. LOICZ Reports & Studies No. 5. Texel, The Netherlands, LOICZ: vi + 96.

Holligan, P. M. and H. e. de Boois (1993). The LOICZ Science Plan. IGBP Report No. 25. Stockholm, IGBP: 50.

Holligan, P. M. (1990). Coastal Ocean Fluxes and Resources. IGBP Report No. 14. Stackholm, IGBP: 53.

Johannes, R. E. (1980). "The ecological significance of the submarine discharge of groundwater." Marine Ecology Progress Series 3: 365-373.

LOICZ (1996). LOICZ Workshop on Statistical Analysis of the Coastal Lowlands Database. LOICZ/WKSHP/96.14. Meeting Report No. 18. Texel, The Netherlands, LOICZ.

Milliman, J. D. (1993). "Production and accumulation of calcium carbonate in the ocean: Budget of a nonsteady state." Global Biogeochemical Cycles 7(4): 927-957.

Milliman, J. D. and A. W. Droxler (1996). "Neritic and Pelagic Carbonate Sedimentation in the Marine Environment: Ignorance is not Bliss." Geologische Rundschau 85: 496-504.

Moore, W. S. (1996). "Large groundwater inputs to coastal waters revealed by ²²⁶Ra enrichments." Nature 380(April 18, 1996): 612-614.

Pernetta, J. C. and J. D. Milliman (1995). Land-Ocean Interactions in the Coastal Zone Implementation Plan. IGBP Report No. 33. Stockholm, IGBP: 215.

Rona, P. A. (1969). "Middle Atlantic continental slope of United States: deposition and erosion." American Association of Petroleum Geologists Bulletin 53(7): 1453-1465.

Smith, S. V. and J. T. Hollibaugh (1993). "Coastal metabolism and the oceanic organic carbon balance." Reviews of Geophysics 31(1): 75-89.

Tribble, G. W. (1990). Early Diagenesis in a Coral Reef Framework. Oceanography. Honolulu, University of Hawaii: 228.

Tribble, G. W., F. J. Sansone, et al. (1992). "Hydraulic Exchange between a Coral Reef and Surface Seawater." Geological Society of America Bulletin 104: 1280-1291.

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