KP-E-PHESTREACH - Methodology

1  Introduction

Information collected from the KP-E-PHESTREACH monitoring program is used for long-term management of the Peel-Harvey system. The sampling regime is set up so that trends are evident over time, not to gain a complete and in-depth understanding of aquatic processes at any particular time. The information presented here is a snapshot - a summary of water quality at each site at the time of sampling. The snapshot cannot be extrapolated from one week to the next; it can only represent what has happened at that place at that time. It is our intention to collate all snapshot information and produce a seasonal/yearly report.

2  Background

Water quality information for this project is to be presented in two different ways - as a concentration or as a category (e.g. low, medium or high). Nutrient levels are presented as a concentration. Algal activity is classified or grouped into the broad categories low, moderate and high. Each category corresponds with a particular concentration of a water quality variable.

Classifying or grouping data into categories usually involves information collected over several years. There is a good reason for this: conditions are rarely similar in two consecutive years. Weather, tides and water run-off vary from year to year as do impacts to the Peel-Harvey system from agriculture, fishing, and urban and industrial developments. Trends can be observed over several years. Abnormal seasonal or monthly data can be identified if a comparison is made with data from the same month in a different year. Without corresponding data from other years, one cannot reliably determine if any data is 'the norm', high or low to date. We have not collected enough data to reliably the algal activity categorise; however, the information presented does provide an indication of what is happening at that time.

3  Sampling regime

There are currently 12 fixed sampling sites (see figure1). The types of data recorded have changed over the life of the project. All sites are monitored fortnightly for phytoplankton, chlorophyll-a and various physical parameters (including dissolved oxygen, temperature and salinity). Nutrients are monitored monthly at 10 sites (the sites PHE58 and PHE02 reflect oceanic nutrient levels).

4  Presentation of data

a Nutrients

The nutrient maps show total phosphorus (TP) and total nitrogen (TN) snapshot data. Coloured squares were used to represent the nutrient concentrations at each site on the map. These coloured squares represent the percentile range the snapshot values fall between (Table 1). Five years of historical data was used to determine the percentile ranges. Each percentile range was designed to capture about one quarter of data; however, some allowance has been made to include the ANZECC 2000 values as range cut off points. Note that 47 per cent and 69 per cent of the TN and TP values respectively are greater than the south-west Australian estuaries ANZECC 2000¹ trigger value. As an example of how one may read the information in table 1, in the last five years less than 24 per cent of TN values are less than 0.51 mg/L and 75 per cent of TN all values are below 1.2 mg/L. When a nutrient sample is analysed for the snapshot, it is compared against the percentile range, then the associated coloured square is used on the map. If, for example, 0.05 mg/L TP is recorded at a site, it will be grouped in the 50-74 per cent range and a dark blue square is displayed on the map.

Table 1 Percentile range and equivalent nutrient concentrations used to determine the map symbols

TN (mg/L)	TN Percentile range	TP (mg/L)	TP Percentile range	Map symbol
< 0.51	0 - 24%	< 0.029	0 - 30%
0.52 - 0.74	25 - 52%	0.03+ - 0.041	31+ - 49%
0.75+ - 1.1	53+ - 74%	0.042 - 0.080	50 - 74%
1.2 <	75 - 100%	0.081%<	75 - 100%

+ Adjusted to align with ANZECC 2000 south-west Australian estuaries value

An assessment of the long-term data is required to present nutrients in categories similar to algal activity.

b Algal activity

The algal activity information is produced by combining several related data sets. Chlorophyll-a and field observations are used to determine the low, moderate or high category for an area. chlorophyll-a is a chemical used by green plants and algae to convert sunlight into energy. chlorophyll-a, when used in conjunction with other measures, may indicate the amount of algae present. The colours green (low), orange (moderate) and red (high) are used to represent the algal activity on the map.

Firstly, the category for each data set is determined and then this information is combined with the other data sets to produce the algal activity category (Table 2).

Table 2 Process used to determine algal activity

Data set		Determine level for data set
Chlorophyll-a		L, M or H*		Combine data		Determine algal activity category
Field observations		Algae seen in estuary

^* Low (L), moderate (M) or high (H)

Percentiles are used to determine chlorophyll-a (Table 3). For example, sample data may be in the lowest 20 per cent of all data collected so far and be categorised as low. The additional value of 0.003 mg/L used as criteria to determine a high category in chlorophyll-a is taken from the ANZECC 2000 south-west Western Australian estuaries trigger values.

Table 3 Data used to produce algal activity reports

^* Low (L), moderate (M) or high (H)

^** ANZECC 2000 trigger value for estuaries in south-west Western Australia

Field observations describe what is visibly occurring at each site. These include water colour, turbidity, scums, water flow, evidence of algae/debris or anything else that may be observed during sampling. While collecting samples and recording water quality are essential for analysis, field observations may provide an overall environmental picture that can 'tie in' much of the other data.

The field observations are interpreted in combination with the chlorophyll-a results. Variations in algal species means that high chlorophyll-a does not necessarily reflect high algal densities (see Limitations). However, combining both data sets provides a stronger case to indicate algae conditions occurring at that site at that time.

5  Limitations

Confidence in algal activity is reduced by the amount of data collected and variations in algal species. Algal activity is based on one year's data, so the categories determined for the Peel-Harvey and associated waters within the project are currently scientifically unreliable. However they can provide a general indication of algal dynamics in the waterway. Periodic reviews of the methodology will include new data and resources to increase the accuracy and reliability of the categorisation process.

By using various data to present algal activity, one would expect to see algae in the water. For example, an area categorised as high would be anticipated to show some evidence of algae in the water. This is not always the case. The categorisation process of algal activity may also be described as 'fuzzy' and subject to errors. Algal species vary in shape, size, environmental effects and amounts of chlorophyll-a. The visible algal activity in the water may differ from the category presented here due to those variations.

For example, high chlorophyll values may have low algal densities because the dominant algal species contains high amounts of chlorophyll. This scenario may be categorised as high algal activity; however, nothing can actually be seen in the water. Why? The actual number of algal cells (algal density) is low - so the water isn't unusually coloured and there isn't any scum on the water.

The reverse is also true. Low chlorophyll-a values may appear to indicate low algal activity; however, the actual algal densities may be high, so a scum is produced or the water appears 'dirty' or turbid. Combining chlorophyll-a with visual observations will reduce this error but the process is not infallible. The data presented in this project is currently the best representation for algal activity; however, there may be instances when algal activity categorisations are not reflected in the environment.

Spatial and temporal patterns of sampling

Both the spatial (where the sampling occurs) and frequency (when the sampling occurs) do not complete a daily picture of the Peel-Harvey Estuary.

The spatial pattern of sampling (figure 1) is different to the locations of many activities occurring in the estuary. The canals and shoreline of the estuary are two examples of areas the sample sites do not cover; yet a majority of housing, recreational and commercial activities on the estuary occur in these areas. The different environmental conditions in the canals and shoreline will lead to different algal growths compared to the sample sites. The sample sites were chosen to maintain the continuity of data from previous projects.

The estuarine sampling run occurs fortnightly, depending on weather. Nutrient sampling occurs on a monthly basis. Tides, wind, water flow, rainfall and boat traffic can influence algal growth and algae can grow, disperse and die off between sampling events.

Figure 1 Spatial pattern of sampling

There is only enough information to quantify algal activity at the sample sites at the time of sampling, in other words, to provide a snapshot of what is occurring. Long-term trends can be identified by combining the snapshots. The current sampling regime is designed to provide results representing long-term changes to the Peel-Harvey estuarine system.

¹ Australian and New Zealand guidelines for fresh and marine water quality 2000 (ANZECC 2000)