September 1980, the effects of salt water cooling towers at the P.H. Robinson generating station on terrestrial plants.
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The five salt water cooling towers were shown to contribute to salt deposition in the surrounding area. Levels as high as 1200 kg salt/ha/yr were encountered within 100 m of the towers. Deposition rates decreased in a logarithmic fashion with distance to less than 300 kg salt/ha/yr at 434 m with only 16% attributable to the cooling towers. The remaining deposition was caused by natural sea spray which varies widely but averages about 250 kg salt/ha/yr in the study area. Changes in composition of air-borne salts with distance were noted, primarily as a narrowing of the Na:Ca ratio. Variations in salt depostions were attributed in part to variations in the chemical composition of the canal water. The soils in the area adjacent to the salt water cooling towers had safe exchangable Na+ and total salt levels. Changes in soil salinity due to the cooling towers after their first four years of operation were found only in the closest study plot at 104 m from the towers. Sodium absorption ratios (SAR) increased over the original SAR values in the area between the cooling towers but not beyond plot number 1. There is some evidence that SAR values in more distant plots may have decreased in 1979 over initial levels due to the high rainfall that occurred that year. After four years only a two fold increase in SAR occurred in soil immediately beneath the towers. A leaching study indicated that the various ions removed from the soil profile were in the same relative proportions as in the soil solution. Continued operation of the salt water cooling towers may eventually lead to relative cation concentrations in the soil solution equal to those in salt deposited for the cooling towers. Therefore, predictions based on cation-exchange equilibria indicate that exchangable Na+ levels greater than 15% will be encountered as far away as 200 m from the cooling towers. This could lead to deterioration of soil physical structure, causing further reduction of the already slow internal drainage, thus enhancing salt accumulation problems. Since most of the salt is deposited within 100 m, salinity at greater distances will be lower and will require longer to develop. The only effect noted as of August 1979 was a buildup of Ca in Plots 3-5. The salt burn symptoms in a variety of ornamental plants is described as the effect of NaCl on the growth rate of 12 species. Calcium sulfate is shown to reduce the effect of NaCl on Coleus x hybridus growth. It is suggested that a similar effect is occuring under field conditions in the HL&P plots where calcium is accumulating. The impact of the cooling towers on vegetation at Chalk Point, Md. is compared with the impact of the HL&P cooling towers at Bacliff. The pre-adaptation of the Bacliff native plants is illustrated by the much higher natural salt loads of these plants when compared to natural salt loads of common plants at the Chalk Point site. Hurricanes, aridity and heavier natural salt deposition have all selected for a salt tolerant native flora in the Bacliff area. The high natural salt level in the Bacliff air and soils along with poor quality irrigation water limit the landscape use of more salt susceptible ornamentals such as sassafras (Sassafras albidum), dogwood (Dornus florida) or red maple (Acer rubrm). As of July 1979, no salt damage to plants outside the HL&P property was attributable to cooling tower induced salt deposition. Within the property, the impact of the induced salt deposition appears to be limited to an area within 100 to 200 m from the tower. The impact of the tower induced salt deposition not only varies with distance but with year. The impact appears to be much greater in a dry year than in a high rainfall year such as occurred in 1979. Cottonwoods (Populus deltoides) and willows (Salix nigra) growing within 100 m of the towers were severely damaged as were many introduced landscape phytometers. Arizona ash (Fraxinus velutina) trees were damaged in plots that were close to the towers but not in more distant plots. Over 700 native plants were collected in eastern Galveston Co. and several range extensions were noted. The dominant shrub in the area is a salt tolerant species (Baccharis halimifolia). Great variation exists in the natural salt deposition in the Bacliff area due to shifting wind patterns and the geography of the area. The Na/Ca ratio in the cooling towers shifts due to rainfall in the area and this in turn influences the chemical composition of the induced salt depositon. The temporal variation in Na, Cl, Ca and Fe in selected phytometers is described and with one exception, no increase in tissue salt level was noted. The effect of various concentrations on NaCl on root growth and top growth of several commonly grown ornamentals was quantified. Significant salt burn symptoms developed after significant growth reductions had already occurred. The beneficial effects of Ca in reducing the effect NaCl on plant growth was noted.