Leonard Robert Gardner

CLIMATE CHANGE, HURRICANES AND TROPICAL STORMS, AND RISING SEA LEVEL IN COASTAL WETLANDS

Global climate change is expected to affect temperature and precipitation patterns, oceanic and atmospheric circulation, rate of rising sea level, and the frequency, intensity, timing, and distribution of hurricanes and tropical storms. The magnitude of these projected physical changes and their subsequent impacts on coastal wetlands will vary regionally. Coastal wetlands in the southeastern United States have naturally evolved under a regime of rising sea level and specific patterns of hurricane frequency, intensity, and timing. A review of known ecological effects of tropical storms and hurricanes indicates that storm timing, frequency, and intensity can alter coastal wetland hydrology, geomorphology, biotic structure, energetics, and nutrient cycling. Research conducted to examine the impacts of Hurricane Hugo on colonial waterbirds highlights the importance of long-term studies for identifying complex interactions that may otherwise be dismissed as stochastic processes. Rising sea level and even modest changes in the frequency, intensity, timing, and distribution of tropical storms and hurricanes are expected to have substantial impacts on coastal wetland patterns and processes. Persistence of coastal wetlands will be determined by the interactions of climate and anthropogenic effects, especially how humans respond to rising sea level and how further human encroachment on coastal wetlands affects resource exploitation, pollution, and water use. Long-term changes in the frequency, intensity, timing, and distribution of hurricanes and tropical storms will likely affect biotic functions (e.g., community structure, natural selection, extinction rates, and biodiversity) as well as underlying processes such as nutrient cycling and primary and secondary productivity. Reliable predictions of global-change impacts on coastal wetlands will require better understanding of the linkages among terrestrial, aquatic, wetland, atmospheric, oceanic, and human components. Developing this comprehensive understanding of the ecological ramifications of global change will necessitate close coordination among scientists from multiple disciplines and a balanced mixture of appropriate scientific approaches. For example, insights may be gained through the careful design and implementation of broad-scale comparative studies that incorporate salient patterns and processes, including treatment of anthropogenic influences. Well-designed, broad-scale comparative studies could serve as the scientific framework for developing relevant and focused long-term ecological research, monitoring programs, experiments, and modeling studies. Two conceptual models of broad-scale comparative research for assessing ecological responses to climate change are presented: utilizing space-for-time substitution coupled with long-term studies to assess impacts of rising sea level and disturbance on coastal wetlands, and utilizing the moisture-continuum model for assessing the effects of global change and associated shifts in moisture regimes on wetland ecosystems. Increased understanding of climate change will require concerted scientific efforts aimed at facilitating interdisciplinary research, enhancing data and information management, and developing new funding strategies.

Origin of the Mormon Mesa Caliche, Clark County, Nevada

On the basis of field and laboratory data described herein, it is concluded that the Mormon Mesa caliche has formed primarily as the result of pedogenetic processes, probably under slowly aggrading, aeolian conditions. The reasons for postulating aggrading aeolian conditions are (1) the absence of A and B soil horizons, (2) the absence of laminated petrocalcic horizons, (3) the lack of quartz grain dissolution and brecciation, (4) the relatively high content of clay and silt in the calcrete (caprock) horizon, (5) the presence of aeolian sand drifts on the present mesa surface, and (6) the presence of fresh red sand in laminated CaCO 3 joint fillings. Also, the aeolian hypothesis may explain the fact that the calcrete horizon of the caliche contains a much greater amount of secondary CaCO 3 than can be accommodated in the original void space of the parent material; and, in addition, the hypothesis avoids the vexing problem, associated with degradational hypotheses, of explaining how water penetrates through the calcrete to form the underlying transition zone of friable caliche. The data further indicates that perhaps at least 25 percent of the secondary CaCO 3 in the caliche was derived from dissolved Ca ++ and HCO 3 − in rainwater, with the remainder probably furnished by aeolian carbonate dust. It is estimated that development of the caliche probably required at least 400,000 yrs and possibly as long as 2,500,000 yrs.

Stratigraphy and geologic history of a southeastern salt marsh basin, North Inlet, South Carolina, USA

Forty seven vibracores and fifteen radiocarbon dates have beenobtained to outline the Holocene history of the North Inlet saltmarsh basin. Marsh deposits date from about 3500 years BP and havetransgressed over a Late Pleistocene beach-ridge terrain that waspartly eroded by Late Holocene tidal channel meandering. Marsh mudalso has prograded southward over shallow subtidal estuarine Macomamuds which date from about 4500 years BP and which are stillaccumulating in adjacent Winyah Bay. The southward migration of themarsh environment probably is due to the southward migration ofboth North Inlet and the mouth of Winyah Bay. The stratigraphy ofthe North Inlet basin offers no evidence for Late Holocene sea-level oscillations.Application of this model of marsh history to the study long-term ecosystem succession driven by slowly rising sea level isdiscussed.

Mobilization of Al and Ti during weathering — Isovolumetric geochemical evidence

Variations in the volumetric concentrations of Al2O3 and TiO2 (in g cm−3) as a function of bulk density for 18 different saprolite suites strongly suggest that significant mobilization of Al and Ti during weathering is more common than is generally assumed. Although trends of decreasing Al2O3 (in g cm−3) with decreasing bulk density could result from dilation, textural and structural features in saprolites argue against significant volume expansion during weathering. Indeed it appears from theoretical calculations that most weathering reactions, including those in which Al is conserved, remove large quantities of various oxides and in the process should create significant amounts of void space. Accordingly, unless large quantities of smectite are produced, it seems unlikely that expansive forces should arise from such reactions. Theoretical calculations are presented that show the effect of dilation on reaction paths. Such calculations are shown to be useful in evaluating the impact of dilation (or compaction) in cases where textural and/or structural criteria are unavailable or ambiguous.

Organic versus inorganic trace metal complexes in sulfidic marine waters—some speculative calculations based on available stability constants

Abstract A theoretical model has been developed in order to test the hypothesis that simple organic acids are the chief agents of trace metal solubility in H 2 S-rich marine waters. The model utilizes stability constant given by Sillen and Martell (1964, 1971) and assumes that the free cation activity of each metal is controlled by simple solubility products. Typical values of pH, pS and Eh are employed in the calculations. The results indicate that free amino acids and hydrocarboxylic acids probably are not effective but that bisulfide and polysulfide complexes may be the chief agents of trace metal solubility. To the extent that it is present, the effect of dissolved organic matter on trace metal solubility probably resides in highly polymerized substances (e.g. humic acids).

A regeneration model for the effect of bioturbation by fiddler crabs on 210Pb profiles in salt marsh sediments

Burrowing by fiddler crabs results in the transfer of sediment at depth to the surface, where it is washed away and replaced by sediment with a surficial 210Pb signature. It is not clear that this mode of bioturbation can be approximated by analogy to molecular diffusion because the exchange is not between adjacent sediment parcels and does not occur in random directions. Accordingly, we propose a regeneration model to simulate the effects of fiddler crab burrowing on 210Pb profiles. The steady-state equation that describes our model is: ∂210Pb∂z=−γ210PbS+KB(210Pb0−210Pb)exp(−z/UB)S where λ is the radioactive decay constant for 210Pb, 210Pb0 is the activity of 210Pb at the surface, S is the sedimentation rate, KB is the burrowing frequency and UB is the mean depth of a burrow. The probability of a burrow reaching or exceeding a given depth z is assumed to be distributed exponentially. Depending on the values selected for KB and UB a wide variety of profile forms can be simulated or fitted to actual data, including profiles that show an abrupt increase in the apparent sedimentation rate at depth using conventional models. We suggest that such profiles could be due to bioturbation rather than actual changes in sedimentation rate. A useful aspect of the model is that it can be used to calculate the volume of sediment turned over each year by bioturbation as a function of depth.

Isovolumetric geochemical investigation of a buried granite saprolite near Columbia, SC, U.S.A.

Saprolites are residual soils which preserve the textures of their parent rocks and thus have evolved by an isovolumetric process of weathering (MILLOT, 1970, The Geology of Clays, Springer). Using bulk density, saprolite elemental analyses can be converted to units of g cm−3. Furthermore, an empirical reaction progress diagram can be constructed for a suite of saprolite samples by plotting element concentrations (in g cm−3) against bulk density (B.D.). Our data for a granite saprolite show that Al2O3 and SiO2 decrease in a linear fashion from B.D. 2.1g cm−3 to 1.5g cm−3 but that K2O follows a curvilinear trend such that it decreases from 75% of its fresh rock value at B.D. 1.6 g cm−3 to nearly zero at B.D. 1.5 g cm−3. The only hypothetical reaction paths that are compatible with these B.D. vs A12O3, SiO2 and K2O constraints are those in which orthoclase alters to kaolinite through an intermediate potassium phase similar to KAl3Si3O10(OH)2 or KAl2Si2O6(OH)3 (hypothetical K-kaolinite). Normative mineral calculations, X-ray diffraction data and structural H2O data are employed to test this conclusion.

The hydrology of Lake Bosumtwi, a climate-sensitive lake in Ghana, West Africa

Abstract Lake Bosumtwi, lying in a million-year-old meteor crater, is hydrologically closed in spite of the wet, humid climate in this part of Ghana. To understand this geographical enigma, a water-balance model that describes both the historical lake-level record and the full range of lake levels observed in terrace deposits around the lake was developed. The water-balance model shows that the reception of rainfall by and evaporation from the lake surface are the dominant constituents of the water balance. Prior to 1969, the average rainfall of 1550 mm year −1 was generally equal to lake evaporation, and the average annual rise of 30 cm year −1 was produced mostly by runoff from the small watershed around the lake. Since 1969, with a decreased rainfall of 1380 mm year −1 , the combination of rainfall and runoff has nearly equaled lake evaporation, resulting in a nearly steady lake level. Long-term simulations show that stochastic climatic variations very similar to those observed in this century could produce the full range of lake levels observed in terrace deposits. The low salinity of about 1‰ suggests that dissolved solutes were removed by lake overflow in the recent geological past.

The role of rock weathering in the phosphorus budget of terrestrial watersheds.

Residual soils (saprolites) developed on crystalline rocks appear to form by an essentially isovolumetric process (i.e. without dilation or compaction). Isovolumetric geochemical analysis of a suite of saprolite samples developed on a common parent rock can be used to estimate the relative rates of long-term losses of P and Si during weathering. Using the export of dissolved Si in rivers as a weathering index, one can then estimate the rate of P release due to chemical weathering by means of the P-Si loss ratio in saprolite. For three basins where data are available (Liberty Hill, SC; Amazon River, Brazil: Rio Negro, Brazil) estimated P weathering release rates are 163, 457, and 242 moles P km−2 yr−1 respectively. These compare to precipitation inputs of 684, 700 and 630 moles P km−2 yr−1 and total river exports of 256, 4490 and 820 moles P km−2 yr−1, respectively. The Rio Negro shows a near perfect balance between the input of P via precipitation and chemical weathering and the riverine output of dissolved and suspended P. This system, however, raised the unsolved problem of the source that supports the atmospheric P input.

The role of groundwater flow in controlling the spatial distribution of soil salinity and rooted macrophytes in a southeastern salt marsh, USA

Groundwater flow is an important factor in governing botanical zonation in the salt marsh at North Inlet, SC. Areas of the marsh adjacent to upland forest are characterized by upward flow of fresh groundwater. This inhibits the infiltration and evapoconcentration of saline tidal water and the development of a habitat for hypersaline-tolerant fugitive species such as Salicornia europaea. Areas of high marsh that are not adjacent to extensive upland forest are characterized by downward gradients in hydraulic head. This allows the infiltration and evapoconcentration of tidal water and the development of hypersaline conditions that are suitable for salt-tolerant fugitives.