[JJ
river health
refereed paper
t
}
a . ! ..
L
..
,~
....
...
'" uo
2"
...
E
·= 7.00 g .., .,. .,.,. :,
E C
8
C
'" 1 ,,. ~~
~
,-
z
.
C 5.1)0
il
,
~
~
';i
l
'" 100
::
9/ll~CHXI
,JU/lOOIOOO
,..,i,20010,00
1/1~0:00
.... o.oo t/lJ/JOOI0.00
Plot 1a. Calculated equivalents for DOC, Turbidity, nitrate and TOC from upstream site. significant period using full spectrum UVNis spect rophotomet ers running o n a 2 minute measurement interval. The locations are about 100 km apart, with numerous tributary streams entering the river along this distance. These tributaries drain intensively farmed areas. In addition, some discharges from dairy and meat processing facilities are also present The data in plot 1a and b shows the general trend in absorption values at these two points. The Upriver point has far lower concentrations of components that absorb in the UVN is spectrum which includes many organics and nitrate. This is reflected in the scales used in the plots. The event not ed as a single peak in upstream data (River 160) and a double peak in the downst ream data (River 290) are al l caused by the same rain event which fell as a broad band moving from dow nstream to upstream. This explains the time difference between the peak on Friday/ Saturday in the River 160 data and the earlier sharp peak in the point 290
,..
-TOC...ffll,/I -HOJ~ffllll
2"
""
';i
-~
,.,.
'·"'
River 290
?...
-
OOC,._ffllll
•.oo
2"
. ,. 1
~
!
,
u.m
';i E C
V
2"
8
i . _,./
~
'6
:e,:!.
,oo
'"
...
t/11/lOOIO:OO
·"z
0.00
t(14/10CMIOCO
t/U/X:0.0-00
t/l l/200l();(IO
Plot 1b. Downriver for same time period.
data. The event noted in the River 290 downstream data at midday on Sunday is the result of the upstream flow from t he peak in River 160 reaching the River 290 point hours later. The river has a speed of greater than 1 m/ s over much of its length. This time difference had already been determined by a large number of events seen in the data over a period of more than 2 years. This then allows us to study the changes in components and concentrations as the material progresses down the river. Short term sudden shifts in solids as seen on the Monday and Tuesday in Plot 1 b indicate events very close to the measuring point and are unlikely to represent w hole of river events. The diurnal variation had been noted previously by grab sampling, The spectral data indicate that the variation is primarily driven by dilution by the varying flows discharged by upstream hydro stations (to match power requirements) with some smaller concentration changes caused by the river ecology. A dilution driven change from a clean source would affect almost all
components in the spectrum whi le a biological change wi ll see an increase in the nitrate spectral absorption during the day as the river biology reacts to sunlight and oxidises ammon ia, with a small correspondi ng reduction in some organics and a rise in others as they are consumed or released by t he biomass. In Plots 2 to 5, the nitrate, which absorbs directly in the UV spectrum, can be considered to be the major contributor to the red/orange coloured components. The data in Plots 2 to 5 below show summer and winter spectral images for the two river locations in Plots 1 a and b. They show that the degree of dilution and biologically driven change varies over the year. There is more biological activity during the warmer summer months, however, the main driver of the visible change, especially in winter, is dilution. In winter t he temperature is lower and sunlight hours reduced w hich slows biological changes. Higher winter power use results in more flow and more flow variation t hrough hydro stations creating a larger dilution factor in the d iurnal variation.
water FEBRUARY 2010 159