Nitrate and phosphorus leaching in New Zealand: a national perspective

Abstract

Excessive amounts of nutrients in rivers promote biological growth of periphyton and macrophytes to nuisance levels. Of most concern, because they are immediately available for growth, are dissolved inorganic forms of nitrogen (N) and phosphorus (P), primarily as nitrate-N and dissolved reactive phosphorus (DRP). To help understand the sources of dissolved nutrients, we estimated and mapped subsurface flow (i.e. leaching) losses of nitrate and DRP.There are large areas of high nitrate leaching in Waikato, Bay of Plenty, Taranaki and Canterbury. The high spatial detail of the maps permits use for planning mitigation at local, regional and national scales. However, they should not be used to infer leaching rates for particular farms as average farming practices are assumed. The nitrate leaching maps were driven primarily by animal numbers, so regional trends of total leached nitrate between 1990 and 2010 were able to be determined from regional statistics of farm animals.

Soil Hydraulic Modeling Outcomes with Four Parameterization Methods: Comparing Soil Description and Inverse Estimation Approaches

“…Within New Zealand, rapid expansion of the dairy industry has coincided with a 17% increase in irrigated land area since 2005 (Statistics New Zealand, 2013) and an estimated 1900 Gg N yr −1 applied as fertilizer (Ministry for the Environment, 2015) to support additional productivity. This intensification of agricultural land use has generated interest in issues surrounding nutrient and contaminant leaching (Dymond et al, 2013; Jiang et al, 2010). Many of these issues are concentrated on the stony, glacial‐alluvial soils of the Canterbury region (Carrick et al, 2013), where variables such as conductivity are known to vary significantly among samples within the same soil type (Webb et al, 2000).…”

Alternative Perspectives on Sustainability: Indigenous Knowledge and Methodologies

“…The three-year project (2016-2018) investigates the ways in which Ngāti Maniapoto (a Māori iwi or tribe in the central North Island) are asserting mātauranga and kaitiakitanga (Māori stewardship according to iwi aspirations and practices) in relation to the co-governance and co-management of the Waipā River. The Waipā River is the major tributary of the Waikato River, New Zealand's longest river, and has been identified as one of the most degraded freshwater systems in Aotearoa New Zealand [33,34]. The Waipā River and its tributaries flow through environments that have been radically changed by human activities over the last 180 years.…”

Reregulating for Freshwater Enclosure: A State of Exception in Canterbury, Aotearoa New Zealand

“…In the past 20 years more than 8000 consents to draw water from streams, rivers and aquifers have been issued by ECan, fuelling the fastest rate of conversion to dairy of any region in recent years; Canterbury now has approximately 70% of Aotearoa New Zealand's total irrigated land (White ; Williams ). However, this conversion has come at a significant cost to freshwater quality and availability, as nutrients leach into waterways (Dymond et al ) and water is drawn from rivers for irrigation.…”