Page 109 - Environmental Control in Petroleum Engineering

96 Environmental Control in Petroleum Engineering

have been observed in coniferous forest growth following blowouts
at distances as great as 2 km from the wellhead (Baker, 1991).

3.3 SALT

Salt (sodium chloride) in low concentrations is essential to the
health of plants and animals. At concentrations different from the
naturally occurring levels found in a given ecosystem, however, salt
can cause an adverse impact.

3.3,1 Impact on Plants

The impact of salt on plants arises primarily from an excess salt
concentration in the cellular fluids of the plants or from an alteration
in the soil structure in which the plants grow. The primary impact of
an abnormal salt concentration in cellular fluids is the disruption of
the fluid chemistry balance within cells. This disruption inhibits
cellular growth, water uptake, and the overall health of the plants.
Growth of nonmarine plants is impaired at total dissolved salt concen-
trations between about 1,500 and 2,500 mg/1, although this threshold
level varies significantly with plant type, how the water is applied,
and whether the soil is kept saturated. Salt concentrations below about
1,000 mg/1 seem to improve some plant growth (Vickers, 1990).
When salt was spread over soil in the form of salty drilling muds,
the yield of brome grass was reduced when the concentration of
chloride exceeded about 1,000 kg Cl/hectare for potassium and sodium
chloride, and about 50 kg Cl/hectare for a freshwater gel. The plant
yield for intermediate chloride application levels was higher than that
of control plots (Macyk et al., 1990).
Salt can indirectly impact plant growth by altering the physical
properties of soil. When saline water is discharged on land, it can alter
the pore structure of the soil by causing compaction, limiting the
access of air and water to the plant roots. The impact varies, however,
with salinity level and plant type. If the total dissolved solids content
is above about 2,800 mg/1, salt can build up in the soil (Vickers, 1990).
Excess sodium in soil can also cause clays to disperse, lowering
the permeability of the soil. This can form an impenetrable surface
crust that hinders the emergence of seedlings and limits the availability
of nutrients such as iron, manganese, calcium, and magnesium to the