Dissolved Oxygen (DO) Data Collation and Preliminary Analysis
Prepared for Ministry for the Environment
January 2016
Prepared by:
Craig Depree
Martin Unwin
Roger Young (Cawthron Institute)
For any information regarding this report please contact:
Craig Depree
Water Quality Scientist - Group Manager
Environmental Chemistry and Ecotoxicology
+64-7-856 1750
National Institute of Water & Atmospheric Research Ltd
PO Box 11115
Hamilton 3251
Phone +64 7 856 7026
NIWA CLIENT REPORT No: HAM2016-008
Report date: January 2016
NIWA Project: MFE15205
Quality Assurance StatementChris Hickey / Reviewed by:
Alison Bartley / Formatting checked by:
John Quinn / Approved for release by:
Contents
Executive summary 10
1 Introduction 14
1.1 Background 14
1.2 Project scope and deliverables 14
2 Methods 15
2.1 Continuous DO 15
2.2 Spot DO 19
3 Summary of DO data 22
3.1 Continuous data 22
3.2 Summary of spot DO data (NEMaR database, Unwin and Larned 2013) 27
3.3 Comparison of the distribution of continuous and spot DO sites 30
4 Preliminary analysis of continuous DO data against current NOF threshold values 33
4.1 Overall ‘picture’ of DO based on continuous data 33
4.2 NOF bands by region 34
4.3 NOF bands by REC classification level 35
5 Exploratory data analysis of spot DO data against current NOF threshold values 41
5.1 All data summary (n=799) 41
5.2 Distribution of DO bands (SPOT-1d and SPOT-7d) by region and REC
classification level 42
5.3 By REC classification level 44
5.4 Effect of sampling time on the difference between spot DO measurements
and actual DO minima 48
6 Summary points 53
7 Acknowledgements 54
8 Glossary of abbreviations and terms 55
9 References 57
Appendix A Continuous DO data request 58
Appendix B Continuous DO data 60
Appendix C Spot DO 74
Appendix D Analysis of continuous data 77
Appendix E Analysis of spot DO data 91
Tables
Table ES1: DO concentration bands (A-D) for daily minimum (NOF-1d) and 7-day
average minimum (NOF-7d) NOF attributes that apply to streams and rivers downstream of point-source discharge. 10
Table 21: Continuous DO data availability by region. 15
Table 22: DO concentration bands (A-D) for daily minimum (NOF-1d) and 7-day
average minimum (NOF-7d) NOF attributes. 17
Table 23: The number of continuous DO data sets (site and season) assessed
against the NOF daily (NOF-1d) and 7-day average (NOF-7d) attributes for DO. 18
Table 24: Selected long-term continuous DO monitoring sites used to analyse diurnal variation in DO. 18
Table 25: Summary of spot DO data from the 799 sites contained in the Phase 3
NEMaR database (Larned et al. 2015). 20
Table 26: The two sets of thresholds used to assign different bands (A-D) to spot DO data. 21
Table 31: Distribution of continuous DO sites (n=368) by region. 23
Table 32: Distribution of the continuous DO sites (post QA, n=367) by REC climate class. 26
Table 33: Distribution of the continuous DO sites (post QA, n=367) by REC topography class. 26
Table 34: Distribution of the continuous DO sites (post QA, n=367) by REC dominant
land cover class. 26
Table 35: Distribution of spot DO sites (n=799) by region (NEMaR database). 28
Table 36: Distribution of spot DO sites (n=799) by REC climate. 30
Table 37: Distribution of spot DO sites (n=799) by REC topography. 30
Table 38: Distribution of spot DO sites (n=799) by REC dominant land over. 30
Table 41: Comparison of A and D bands for NOF-1d (n=367), NOF-7d (n=111) and
NOF-1d (n=111) grouped by REC climate class. 37
Table 42: Comparison of A and D bands for NOF-1d (n=367), NOF-7d (n=111) and
NOF-1d (n=111), grouped by REC land cover class. 39
Table 51: Proportion of 'at risk' sites with D or C bands (based on SPOT-7d
thresholds) within each region. 44
Table 52: Proportion (%) of 'at risk' sites with D or C bands (based on SPOT-7d thresholds) within each REC climate class. 44
Table 53: Proportion (%) of 'at risk' sites with D or C bands (based on SPOT-7d thresholds) within each REC topography class. 46
Table 54: Proportion (%) of 'at risk' sites with D or C bands (based on SPOT-7d thresholds) within each REC land cover class. 47
Table 55: Maximum ‘DO offset factors’ using 5th and 50th percentile DO
oncentrations for the 9 sites shown in Figure 57. 51
Table A1: List of recipients (and their affiliation) of the request for continuous data. 59
Table B1: Distribution of continuous DO sites (n=367) by region and REC climate classes. 60
Table B2: Distribution of continuous DO sites by region and REC topography classes. 60
Table B3: Distribution of continuous DO sites by region and REC dominant land cover classes. 61
Table B4: Details of all sites that were included in the continuous DO data collation (n=489). 62
Table C1: Duration of spot DO records (2000 onwards) by region. 74
Table C2: Distribution of spot DO sites (n=799) by region and REC climate classes. 75
Table C3: Distribution of spot DO sites (n=799) by region and REC topography class. 75
Table C4: Distribution of spot DO sites (n=799) by region and REC dominant land
cover class. 76
Table D1: DO minimum and corresponding NOF-1d band for continuous DO sites (n=368). 77
Table D2: NOF-1d band assignments from continuous data (n=368) grouped by region (RC). 89
Table D3: NOF-1d band assignments from continuous data (n=367) grouped by REC climate class. 89
Table D4: NOF-1d band assignments from continuous data (n=367) grouped by REC topography class. 90
Table D5: NOF-1d band assignments from continuous data (n=367) grouped by REC
land cover class. 90
Table E1: Different DO band thresholds applied to spot DO data (n=799) and
grouped by region. 91
Table E2: Different DO band thresholds applied to spot DO data (n=783) and
grouped by REC climate class. 92
Table E3: Different DO 'attribute' thresholds applied to spot DO data (n=783) and grouped by REC topography class (SPOT-1d upper; SPOT-7d lower). 93
Table E4: Different DO 'attribute' thresholds applied to spot DO data (n=783) and grouped by REC land cover class. 93
Figures
Figure ES1: Comparison of DO state (all data) determined from continuous (NOF-1d
and NOF-7d) and spot (SPOT-7d) DO data. 11
Figure ES2: DO state by region, based on spot data (for n=799 sites) using SPOT-7d thresholds. 11
Figure 11: Example of 24-hr (diel) variation in dissolved oxygen in a river. 13
Figure 21: Diurnal curve for the Waikato River at Hamilton traffic bridge (WRC data). 18
Figure 22: Sites affected if filter applied to exclude sites that contain <36 DO measurements (2000-) . 20
Figure 31: Duration (years) of continuous DO data sets for the 368 sites. 21
Figure 32: Duration (days) of discrete seasonal (NOF summer) continuous DO data (n=614). 22
Figure 33: Geographical distribution of continuous DO monitoring data sets (sites) collated in the DO database. 23
Figure 34: Geographical distribution of NOF-1d (n=368, orange) and NOF-7d (n=112,
blue) sites. 24
Figure 35: Distribution of spot DO dataset duration (n=799) for records from 2000 (inclusive). 26
Figure 36: Geographical distribution of spot DO sites from NEMaR database (Larned
et al. 2015). 28
Figure 37: Comparison of the by region distribution of spot (y-axis) and continuous (x-axis) DO sites. 30
Figure 38: Distribution of continuous (blue) and spot (green) DO sites by REC climate class. 30
Figure 39: Distribution of continuous (blue) and spot (green) DO sites by REC topography. 31
Figure 310: Distribution of continuous (blue) and spot (green) DO sites by REC climate. 31
Figure 41: Overall national summary of NOF DO bands (daily and 7-day average). 32
Figure 42: NOF-1d and NOF-7d threshold bands, emphasising the relative difference in 'concentration width' of B and C bands. 33
Figure 43: Distribution of NOF-1d DO bands by region. 34
Figure 44: Distribution of NOF-1d (daily) band assignments from continuous data
(n=367) by REC climate class. 34
Figure 45: Distribution of NOF-7d (upper) and NOF-1d (lower) bands (for n=111 sites
with >7day duration) by REC climate class. 35
Figure 46: Distribution of NOF-1d (daily) band assignments from continuous data
(n=367) by REC topography class. 36
Figure 47: Distribution of NOF-7d (upper) and NOF-1d (lower) bands (for n=111 sites
with >7day duration) by REC topography class. 37
Figure 48: Distribution of NOF-1d (daily) band assignments from continuous data
(n=367) by REC dominant land cover class. 38
Figure 49: Distribution of NOF-7d (upper) and NOF-1d (lower) bands (for n=111 sites
with >7day duration) by REC dominant land cover. 39
Figure 51: Summary of DO bands from applying the SPOT-1d and SPOT-7d (aka
NOF-1d and NOF-7d) sets of threshold concentrations to all 799 spot DO sites. 40
Figure 52: Proportion (%) of SPOT-1d (upper) and SPOT-7d (lower) DO bands (for
n=799 sites) grouped by region. 42
Figure 53: Distribution of SPOT-1d (upper) and SPOT-7d (lower) DO bands (for n=783 sites) grouped by REC climate class. 44
Figure 54: Distribution of SPOT-1d (upper) and SPOT-7d (lower) DO bands (for n=783 sites) grouped by REC topography class. 45
Figure 55: Distribution of SPOT-1d (upper) and SPOT-7d (lower) DO bands
(n=783 sites) grouped by REC dominant land cover class. 46
Figure 56: Distribution of sampling times (grouped by hour) for the 799 sites in the
spot DO database. 47
Figure 57: Diurnal curves (left side) for selected long-term continuous DO sites based
on 5th (orange) and 50th (blue) percentile DO concentrations; and
distribution of spot DO sampling times (right side). 49
Figure A1: The continuous DO data request form sent out to potential providers on
28 May 2015. 58
Dissolved Oxygen (DO) Data Collation and Preliminary Analysis
Executive summary
Introduction
The Ministry for the Environment (MfE) are considering whether the current dissolved oxygen (DO) attribute in the National Objectives Framework (NOF) should be extended to apply everywhere (including from diffuse sources), rather than just downstream of point sources. This first stage of an MfE-funded project was to determine whether there are sufficient continuous DO data to satisfy the 4th guiding principle for NOF attributes – is there data of sufficient quality, quantity and representativeness to assess the current state of the attribute on a national scale?
The concentration of dissolved oxygen (DO) in water is a critical component affecting the life supporting capacity of a river system. Dissolved oxygen concentrations are affected by three key processes: 1) oxygen production associated with photosynthesis of algae and other aquatic plants, which raises the oxygen concentrations within the water, 2) oxygen uptake associated with respiration of all river life including fish, invertebrates, algae, aquatic plants and microbes, which lowers the oxygen concentrations in the water, and 3) oxygen diffusion through the water surface, which can either raise or lower oxygen concentrations, depending on whether the water is under- or over-saturated with DO. Rates of photosynthesis vary with the amount of sunlight available, so DO concentrations can vary widely over a 24 hour period.
Methods
A request for continuous DO data was sent to regional authorities on 28th May 2015. Data that met QA/filtering criteria were assessed against the existing band thresholds for both the NOF daily minimum (NOF-1d) and 7-day average minimum (NOF-7d) DO attributes (Table ES1). An existing NEMaR dataset was used to extract spot DO data, and these data were evaluated against the NOF-1d and NOF-7d thresholds (Table ES1). To avoid confusion with NOF nomenclature, the resulting bands are referred to as SPOT-1d and SPOT-7d ‘attributes’. To account for the tendency of spot DO data to be greater than the true diurnal minimum, ‘C’ and ‘D’ bands were combined to give an ‘at risk’ classification, to improve comparability with NOF-1d ‘D’ band classifications. Multi-year sites were assigned an overall band by taking the median (continuous) or mean (spot) value of the annual summer (Nov-Apr) DO minima.
Table ES1: DO concentration bands (A-D) for daily minimum (NOF-1d) and 7-day average minimum (NOF-7d) NOF attributes that apply to streams and rivers downstream of point-source discharge.
band / Daily minimum (NOF-1d) / 7-day average minimum (NOF-7d)A / >7.5 / >8
B / 5-7.5 / 7-8
C / 4-5 / 5-7
D / <4 / <5
In response to our request for continuous DO data, we received raw data for 489 sites from 14 agencies (12 regional authorities, Cawthron and NIWA). Data were filtered for those occurring within the summer period (Nov-Apr inclusive), based on the assumption that DO minima are most likely to occur in summer when instream plant biomass and water temperature is high and flows are generally low. Summer time-series plots were then visually inspected for spurious data and other anomalies, which reduced the number of continuous DO sites to 368.
Of the 368 continuous sites, 112 were suitable for calculating the 7-day mean DO minimum (NOF-7d). While there was good coverage of continuous DO sites throughout most of the country, unrepresented areas included Northland, Taranaki and East Cape area of the North Island, and north east and south west areas of the South Island.
It is worth noting a couple of caveats regarding the use of the collated continuous DO data for determining the national state of DO in stream and rivers. (1) In general,[1] the data supplied had not been subject to quality assurances (QA) procedures. A preliminary ‘data checking’ procedure was employed for this project. This involved visual screening of all time-series plots to identify potentially anomalous data, such as spikes, missing data, drift and generally ‘odd’ profiles. (2) Individual regions may undertake continuous DO monitoring for different reasons. For example, some agencies may use it for general monitoring purposes,[2] whereas other regions may initiate continuous DO monitoring in response to known DO issues.[3] Indeed, data from 60% of the sites were collected for research purposes aligned with specific projects. Accordingly, the state of DO derived from continuous data may not necessarily be representative of DO quality for a particular region, or on a national scale. Despite these caveats, this first phase of the DO project represents a valuable first step in assimilating the large amount of continuous DO data that has collected by regional authorities and other science providers throughout the country.