Water and Soil - Project Planning and Management for Ecological Restoration - page 103

alive. As water becomes unavailable at the upper levels of the soil, roots are able to move down the
soil column following the receding moisture. This trait improves the survival probability of most
desert plants beyond the rainfall season. Some arid land plants, such as mesquite and juniper, are
able to drop roots in excess of one hundred feet below the surface.
Duration and frequency of irrigation are the most important components of an irrigation strat-
egy. Soil type and temperature are major environmental factors that determine the frequency
and duration of irrigation. Watering too long at a time will provide a saturated soil condition near
the surface and not force the root systems to grow downward. Shallow roots are typical for some
species, such as willows, which are typically found near flowing streams with groundwater several
inches below the surface. The preferred irrigation schedule is to create a pulsing regime whereby
the water column is not totally saturated but is allowed to become drier near the surface as the
water moves downward from evaporation, transpiration, and infiltration. This method of irrigation
facilitates root growth downward toward more permanent water sources.
Frequency of watering is another critical factor for successful growth. The variability of the site
and the many environmental factors on-site require that you examine the plants and let the signs
exhibited by them determine your watering frequency. In many arid regions, water, seeds, scar-
ification, and absence of predation occur simultaneously, permitting the establishment of plant
species. Restoration of an arid area outside of this simultaneous occurrence will require consider-
ation of supplemental watering and how it interacts with the existing porous soil. In many cases,
a single major storm event is enough to load the soil column with sufficient water to supply the
young plants and the root systems that rapidly grow down to significant depths.
The movement of water is much faster in soil with high sand content. In some soils, the water may
actually pass through the root zone so quickly that it is not available long enough for plants to benefit.
Water Chemistry
Water chemistry is often not considered in the early stages of project planning. The existence of
a lake or stream on-site is no assurance of suitable water. Our example in chapter 14 describes the
challenge of using pond water following a five-year “drought” causing a buildup of salts in the ad-
jacent pond water. Soil type and duration of watering are factors affecting whether it is appropriate
to use water with unusually high concentrations of salts.
Commonly, situations exist that preclude one from closely following the principles of ecological
restoration. Modified terrain and the presence of human habitation sometimes dictate making ad-
justments and adapting to the current conditions. Such is the case in Jamaica Bay, New York, where
a significant program of projects has been under way to clean the water of the bay. The municipal
wastewater and stormwater systems are contributing to the decline in water quality and negatively
affecting benthic and other animals throughout the bay (box 7-3). The magnitude and severity of
the challenge demand some rather novel engineering solutions as well as adapting biological re-
sources to contribute to restoring the water quality of Jamaica Bay. In addition, several projects have
been implemented to retard shoreline erosion and establish marshlands to maintain the shorelines
at several locations within Jamaica Bay.