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Reports

The following reports make up the Physiographics of Southland project. They detail the substantial scientific research, validation work, and mitigation and management options that underpin this project.

On this page:

  • Physiographics of Southland Part 1: Delineation of key drivers of regional hydrochemistry and water quality
  • Physiographics of Southland: Development and application of a classification system for managing land use effects on water quality in Southland
  • Physiographic Zones for the Southland Region: Classification system validation and testing report
  • Management practices and mitigation options for reducing contaminant losses from land to water

Delineation of key drivers of regional hydrochemistry and water quality

Part 1 of the Physiographics of Southland project aimed to better understand the ‘drivers’ of hydrochemical variation. That is, why we see variation in hydrochemistry occurring across the region. For this project we only looked at surface water and shallow, locally soil-influenced groundwater as this is where we see declines in water quality resulting from human activity.

Physiographics of Southland - Part 1 - Delineation of key drivers of regional hydrochemistry and water quality (PDF, 12.7 MB)

Technical Chapters (TC) - support the conceptual model and key driver maps presented in the main report.

Appendices and References (PDF, 5.01 MB)

Glossary (PDF, 391 KB)

Abstract

The key aim of this work was to better understand and estimate spatial variation in freshwater hydrochemistry at a regional scale in Southland, New Zealand using a physiographic approach.

We developed a semi-quantitative, mechanistic conceptual model to estimate the hydrochemical variation in ground- and surface waters and shallow, soil influenced groundwater on the basis of four key drivers: (i) precipitation source; (ii) recharge mechanism and water source; (iii) combined soil and geological redox potential, and; (iv) the combination of geomorphic setting and substrate (rock or biological sediment) composition. We applied a multi-element, multi-isotope approach to 28,548 individual samples to identify critical characteristics of existing spatial frameworks (for soil, geology, topography, hydrology and hydrogeology) to resolve key spatial drivers over the hydrochemical variation of surface water and shallow, soil influenced groundwater.

The model was validated through stratification of hydrochemical data using maps spatially depicting variance in key drivers, and independent empirical modelling. Empirical testing indicated a strong estimation capacity for surface water hydrochemistry, but was weaker for groundwater. Nonetheless, the patterns of hydrochemical response for groundwater were still consistent with the model. Furthermore, given a regional, median base flow index of 0.47 the strong performance of the model for surface water indicates the characterisation of young, soil zone influenced groundwater across Southland is robust.

We conclude that the conceptual model is a sound platform for understanding and explaining the spatial controls over hydrochemistry outcomes in Southland. This work provides a spatially resolved platform for the development of a risk based framework for regional landuse. Future work will look at the use of the key drivers as a basis for modelling of transient water and nutrient flux.

Development and application of a classification system for managing land use effects on water quality in Southland

This report establishes a classification system that groups land areas into physiographic zones based on water quality risk.

Physiographics of Southland: Development and application of a classification system for managing land use effects on water quality in Southland. (PDF, 7.6MB)

Synopsis

A classification system for managing water quality risk has been developed for the Southland region for use in Environment Southland’s proposed Southland Water and Land Plan. For the purpose of this report, water quality risk is associated with four main contaminants: nitrogen, phosphorus, sediment and microbes. The classification system comprises 9 physiographic zones (or classes) and 8 variants (or sub-classes). Each zone describes areas with similar characteristics that determine water quality risk.

Water quality risk for each physiographic zone and variant was identified using assessments of their drainage pathways, and the potential for attenuation or dilution processes to occur along each pathway. This water quality risk assessment was then used to identify appropriate mitigation measures to reduce the effects of land use on water quality to support implementation of the proposed Southland Water and Land Plan. Understanding differences between zones allows for targeted land use and management strategies to be developed to reduce impacts on water quality.

Classification system validation and testing report

This report assesses whether the physiographic units used for the proposed Southland Water and Land Plan represent unique assemblages of drivers, environmental characteristics and observed water quality states.

Physiographic Zones for the Southland Region: Classification system validation and testing report. (PDF, 1.47 MB)

Executive Summary

Environment Southland have established a spatial framework for managing land use activities using nine non-contiguous physiographic units. The physiographic units have been mapped according to a conceptual model that relates biogeochemical and hydrological processes that determine potential water quality states to inherent characteristics of the Southland landscape. This report describes tests of the mapped physiographic units that comprised three components:

  • General ‘omnibus’ tests to assess whether the physiographic units represent unique assemblages of drivers, environmental characteristics and observed water quality states;
  • Tests of differences in individual water quality variables to determine the extent to which the physiographic units explain spatial variation in magnitudes and temporal variability in water quality; and,
  • Hypothesis testing to assess the validity of specific expectations for water quality variables that arise from the conceptual model that underpins the physiographic units.

The results show physiographic units strongly discriminate unique combinations of the drivers and characteristics, and that differences between units were strongest where recharge mechanism differed. Variation in the characteristic magnitudes of assemblages of river water quality data were well explained by the physiographic units. The characteristic magnitudes of assemblages of groundwater quality variables was less well explained by the physiographic units. This may reflect better characterisation of river water quality due to more frequent sampling compared to groundwater. The better performance of the physiographic units for river water quality may also be because river sites represent an integrated measure of the overall hydrological and biogeochemical characteristics of the physiographic units occurring across the upstream catchment area, whereas groundwater sites represent a single point in what may be a rather heterogeneous system.

Tests showed that physiographic units strongly discriminate between site differences in the magnitudes of individual water quality variables, particularly for river water quality. The physiographic units also discriminated between site differences in temporal variation (overall variability and seasonal variation) of many individual water quality variables. However, the physiographic units did not explain variation between sites in temporal variability of the groundwater quality variables. It is expected that the physiographic unit variants (sub-units) will increase the explanation of overall variability and seasonality of water quality of the physiographic units. However, the variants could not be tested in this study due to limitations in the availability of water quality data.

Tests of hypotheses concerning expected differences in the magnitude of individual water quality variables between, and within physiographic units were largely consistent with expectations developed from the conceptual models for individual physiographic units (Hughes et al., 2016a). Tests of hypotheses concerning the variability and seasonality of individual water quality variables were rarely inconsistent with the conceptual water quality risk framework (Hughes et al., 2016b), but were often inconclusive due to a lack of data.

Management practices and mitigation options

This gives detailed descriptions of mitigations specific for each zone.

Management practices and mitigation options for reducing contaminant losses from land to water (PDF, 0.4Mb)

Background

This document provides a brief description of a range of good agricultural management practices and mitigation measures that are relevant to managing water quality in Southland. This overview was commissioned by Environment Southland as supporting to help underpin the Council’s proposed Southland Water and Land Plan to be notified in 2016. It draws on a range of generic documents, scientific reports and publications that document the range of potential measures land users can implement to improve water quality outcomes. Section 2 firstly describes general mitigation measures for improving nutrient and effluent management and capturing or attenuating nutrients. Section 3 then provides an overview of mitigation measures that are either targeted at managing critical source areas of contaminant losses (section 3.1) or reducing the accumulation of surplus N in the soil, particularly during autumn and winter (section 3.2).