Location: Southern Horticultural ResearchTitle: Characterization of water quality in stratified nursery recycling irrigation reservoirs.
|ZHANG, HAIBO - Virginia Polytechnic Institution & State University|
|RICHARDSON, PATRICIA - Virginia Polytechnic Institution & State University|
|BELAYNEH, BRUK - University Of Maryland|
|RISTVEY, ANDREW - University Of Maryland|
|LEA-COX, JOHN - University Of Maryland|
|HONG, CHUAN - Virginia Polytechnic Institution & State University|
Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2015
Publication Date: 10/1/2015
Citation: Zhang, H., Richardson, P.A., Belayneh, B.E., Ristvey, A., Lea-Cox, J., Copes, W.E., Hong, C. 2015. Characterization of water quality in stratified nursery recycling irrigation reservoirs.. Agricultural Water Management. 160:63-83.
Interpretive Summary: Water pH in recycling irrigation reservoirs (RIRs) has been shown to fluctuate diurnally and seasonally, and is known to prominently impact nutrient availability, plant pathogen survival, and efficacy of water disinfection treatments. The objective of this research was to characterize detailed patterns of pH fluctuations in nine RIRs located in three states (Virginia, Maryland and Mississippi) for the purpose of developing methods to manage irrigation water quality. The dominant pH levels in RIRs ranged from 6 to 11. Single reservoir recycling systems receiving runoff directly from production area had higher (basic) pH levels the majority of time, in contrast to a natural stream that had a lower (acidic) pH. Within the same reservoir, surface pH levels were higher during summer thermal stratification periods than during winter non-stratification periods. In a stepwise recycling system, pH levels and the daily duration of basic pH levels declined in each RIR that received water flow only from the previous reservoir in series. Implications in water management include priority in selecting a water source for irrigation, pond structure considerations for stepwise water flow systems and single reservoir systems to reduce survival of Phytophthora species, water acidification considerations, and regional differences in pond management. This information will benefit Ag production farms that recycle water for crop irrigation, crops advisors, state extension specialists, and researchers.
Technical Abstract: Water pH is one of the most critical parameters in recycling irrigation reservoirs (RIRs), because of its impact on nutrient availability, plant pathogen survival, water disinfection and pesticide performance. Water pH in RIRs fluctuates dramatically diurnally and seasonally. However, the dominant pH levels and persistence of these levels has not been well examined. This study investigated water pH in nine RIRs located in three states (Virginia, Maryland and Mississippi in USA). The presence and absence of thermal stratification (stratification vs non-stratification periods), climate conditions (Mid-Atlantic vs warmer temperate Gulf Coast climate region) and system design (single reservoir recycling system vs stepwise water flow recycling system) were examined for their influence on pH level and persistence in RIRs. Our results show that the dominant pH levels in RIRs spanned between 6 and10, with 60% in the basic range and the a duration mostly less than 24hrs. Such pH levels differ from normally acidic natural streams . Within the same reservoir, surface pH levels were higher during stratification periods than in non-stratification periods. The reservoir under warmer temperate climate had higher pH levels (dominant pH greater than 9) than reservoirs under the Mid-Atlantic climate (dominant pH between 7 and 9), with less than 1% having acidic pH. Single reservoir recycling systems receiving runoff directly from production areas had over 60% of pH distributions in the basic range. In contrast, a stepwise water flow recycling system had reduced pH levels along the sequence of reservoirs. The proportion of basic pH declined from 69.2% in the first reservoir (VA21), to 32.9% in the second reservoir (VA22) and further down to 14.5% in the last reservoir (VA23). The corresponding duration of basic pHs also declined. This study examined the range and duration of pH levels encountered in agricultural aquatic ecosystems, confirming the observations of pH fluctuations in RIRs in a separate study. The results have several implications in water management. Selection of water source (stream vs RIRs) for a specific purpose is the first consideration in the water management process. In cases when RIR is the only water available, a stepwise water flow recycling system should be considered to reduce pH if not limited by land and expense. Extending retention time of recycled water in single reservoir recycling system could reduce the population of some Phytophthora species. The amount of acid needed to acidify water should be adjusted according to pH and alkalinity levels, as pH is lower during non-stratification periods than stratification periods for the same reservoir.