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compositions in the two systems are quite different. Apart from various species of
water boatmen that occur in both systems, the most abundant macroinvertebrates at
Old Castle were chironomids, midge larvae (Orthocladiinae (subfam.)) and common
darter (dragonfly) (Sympetrum striolatum), compared with bivalves (Anodonta spp.),
caddis larvae (Dicranota spp.), shrimps (Gammarus spp.) and flies (Leptocera
humida) at Langside. The dominant plant species were floating sweet-grass (Glyceria
fluitans) (28%) and Yorkshire fog (Holcus lanatus) (22%) at Old Castle, common reed
(Phragmites australis) (55%) at Langside and water horsetail (Equisetum fluviatile)
(49%) at Black Loch, where the figures in brackets are the relative abundances for
the overall sample.
Black Loch appears impoverished for most indicators compared with the other two
systems; its high total macroinvertebrate abundance is due to the dominance of
water fleas (Bosmina sp.), accounting for 66% of individuals. Comparison of the
ASPT values with SEPA’s Scottish River Classification System indicates that water
quality is ‘fair’ (Class B) in the Old Castle and Langside systems and ‘poor’ (Class C)
in Black Loch.
DISCUSSION
Detailed flow and water quality monitoring at Langside suggest that mature onstream
ponds/wetlands can be sources of nutrients as well as sinks at certain times of
year. This variable efficiency of wetlands has been observed in other pond/wetland
systems receiving agricultural run-off (Table 3).
Table 3:
Performance of other pond/wetland systems treating agricultural
run-off/wastewater
Reference and study information
Braskerud (2002): instream wetlands receiving
arable and dairy run-off, Norway
Dunne et al. (2005b): constructed wetland
treating dairy farmyard water, Ireland
Fink and Mitsch (2004): restored wetland
receiving arable and forest run-off, USA
Geary and Moore (1999): pond-wetland
system for dairy wastewater, Australia
Kadlec (2003): review of 21 lagoon-wetland
systems, North America
Raisin and Mitchell (1995): constructed
wetland treating livestock run-off, Australia
Reddy et al. (2001): experimental marsh-pond
system for swine wastewater, USA
Thorén et al. (2004): constructed pond-marsh
treating agricultural/urban run-off, Sweden
% mass removal: mean (min – max
values)
SS NH 4
-N Total N Total P
65
(27–93)
21-44
(5–84)*
41† 28
26
(3.2–45)
50
(–33–99)
28
(–8.6–57)
49
(7–99)
(–25–40) (–15–45)
66–69 43–60‡ 37–51 31–44
17
(6–36)§
*SRP: 5% removal in winter; 81–84% removal rest of year. †Nitrate N. ‡Most removed
in warmer months. §Annual removal, but 40% of annual N removal exported February
to March 2001.
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