As part of our research at The Maru we
monitor the water quality of three local rivers; the Kande River, the Masembe River
and the Fua River. This month, alongside collecting data on water temperature,
current, turbidity, pH and TDS (total dissolved solids), we have introduced a
Stream Assessment Scoring System (miniSASS) to our water quality monitoring.
This is a tool used to monitor the health of a river and measure the general
quality of the water. MiniSASS scores the sensitivity to water quality of
various macro-invertebrates living in rivers and classes the health of the
river using five categories ranging from natural to very poor.
MiniSASS method:
At each site a small net is held in the
current. Whilst ranging across the river to different habitats; stones,
vegetation, sand etc. are disturbed using your feet or hands. After five
minutes the content of the net is emptied into a white tray filled with some
water. Using a magnifying glass, each insect is studied and identified using
the dichotomous key (Figure 1). We are not concerned with the number of
insects; we are simply interested in the presence or absence of a group. Each
group found scores a certain number based on its sensitivity (Table 1). The sum
of the sensitivity scores for each group found at the site is then divided by
the number of groups to give an average. This average score is compared to the
Ecological Category Table (Table 2) which tells us which health class the river
is in.
Figure
1
The
Dichotomous Key
Table
1
Sensitivity
Score Table
Groups
|
Sensitivity Score
|
Flat worms
|
3
|
Worms
|
2
|
Leeches
|
2
|
Crabs or shrimps
|
6
|
Stoneflies
|
17
|
Minnow mayflies
|
5
|
Other mayflies
|
11
|
Damselflies
|
4
|
Dragonflies
|
6
|
Bugs or beetles
|
5
|
Caddishflies
|
9
|
True flies
|
2
|
Snails
|
4
|
Total Score
|
76
|
Number of groups
|
13
|
Average Score
|
5.8
|
Table
2
Ecological
Category Table
Ecological category (condition)
|
River category
|
|
Sandy
|
Rocky
|
|
Unmodified (natural)
|
>6.9
|
>7.9
|
Largely natural/few modifications (good
condition)
|
5.8-6.9
|
6.8-7.9
|
Moderately modified (fair condition)
|
4.9-5.8
|
6.1-6.8
|
Largely modified (poor condition)
|
4.3-4.9
|
5.1-6.1
|
Seriously/critically modified (very
poor)
|
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|
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Whilst this water quality monitoring
technique is still very new for The Maru, we have already found some
interesting results. So far all of our sample sites fall in the ecological
categories between unmodified (natural), and largely modified (poor condition).
For examples as Figure 1 shows, the health class of each site along Kande River
has varied from natural to poor within 4 weeks. More data is needed in order to
see if this will stabilise and how conditions may vary seasonally. However, it
is good to see that the majority of the samples (75%) are either ‘natural’ or
‘good’ and a smaller proportion of the data (25%) fall in the ‘fair’ and ‘poor’
categories.
Figure 1. Graph showing
the health class of 4 sites along Kande River over 4 weeks where an ecological
score of 1 is ‘natural’, 2 is ‘good condition’, 3 is ‘fair condition’, 4 is
‘poor condition’ and 5 is ‘very poor’.
Our data will be uploaded onto the miniSASS
website (www.minisass.org) in order to help map river health across Southern
Africa. Once more research has been done using this method, communities can use
the information and knowledge of the rivers to investigate why the river is in
good condition and how to keep it that way or to identify pollution sources in
areas of poor condition. Locals are already very interested and curious and
enjoy learning about what we are doing and having a look at the insects we
find.
(This post was written by by Karin Johannson one of our current interns! Good job Karin! To find out how you can intern or volunteer with us just CLICK HERE)
