PROCESO CREDITICIO 71

All the weekly chemical data were initially subject to an ion balance to establish basic quality control. At this stage problems with sulphate determinations during 1982 became apparent and thus no results are reported for that year. For all other years samples with an ion balance greater than +/-10% were rejected.

Estimates of annual input loadings (kg ha-1 yr-1) were initially calculated as the product of the volume-weighted mean annual concentration of each element in the collector (mg l'1) and the total annual precipitation (cm). Total annual precipitation was calculated separately for each sub-catchment using a height-weighted method which assumes a linear increase in precipitation, at the Loch Dee sites, of 6% per 100m increase in altitude (Welsh and Burns 1987). However, the determination of inputs solely from bulk precipitation data probably underestimates the additional input of elements through dry deposition. Consequently, to improve the accuracy of the input loadings dry deposition rates for the major cations were estimated by assuming that chloride is chemically conservative within the sub-catchments, so that the annual net output of chloride is balanced by dry deposition. The dry deposition rates of the major cations were then calculated following Clarridge (1970), who demonstrated that the ratios of the major cations to chloride in dry deposition is identical to those in the bulk collector. Thus the dry deposition rates of the major cations were determined by multiplying the ionic ratios to chloride in precipitation by the net chloride output (Wright and Johannessen 1980).

Annual solute outputs (kg ha-1 yr-1) were determined using rating curves for those ions which registered a statistically significant relationship (p>0.95) between flow and concentration (Table 5.1). The resulting daily solute outputs were derived as the product of the mean daily flow and the associated concentration divided by the appropriate sub-catchment area. When summed these values produce the annual output for each ion. This output value was then corrected for statistical bias using the procedure developed by Ferguson (1987). As

species Equation R2 s.e.e

White Laggan Burn

H+ _{H = 3.63 Q °-53 0.65 0.303} Ca++ _{Ca = 52.48 Q’0-16} 0.55 0.096 Mg _{Mg = 57.54 Q-0-09 0.46 0.098} Al Al = 18.20 Q °-20 0.41 0.177 SiO2 Si = 2.67 Q-0.11 0.35 , 0.107

Dargall Lane Burn

H _{H = 23.44 Q °-69 0.73 0.279} Ca++ _{Ca = 26.30 Q-0-22 0.59} 0.098 Mg _{Mg = 38.91 Q-0-10 0.33 0.084} Al . Al = 38.02 Q °-32 0.60 0.134 SiO2 Si = 3.03 Q'°-14 0.43 0.090 Green Burn H _{H = 22.89 Q °-91 0.88 0.206} _ ++ Ca _{Ca = 39.81 Q-0-17 0.47 0.102} ,. ++ Mg _{Mg = 48.98 Q~0-14 0.44 0.098} Al Al = 40.32 Q °-25 0.54 0.158 SiO2 Si = 3.54 Q-°-19 0.55 0.107

Table 5.1: Regression relationships between concentration

(ueq/1) and discharge (Q, m3/s) which are

statistically significant at p>0.95.

.E<pia£ ion;

Qdl = 0-361 Qwl R2 _ o,96 s.e.e = 0.084 Qgb = 0.431 Qwl 1-02 R2 = 0.98 s.e.e = 0.096

Table 5.2: Regression relationships between mean daily flows on the Dargall Lane (QDL) and Green Burn

(Qgb) and mean daily flows on the White Laggan (Owl) • (Flow measured in m3/s)

the Dargall Lane and Green Burn have only been gauged since July and September 1983 respectively, retrodictive models to produce mean daily flows for earlier periods were developed. These models took the form of regression equations in which the mean daily flows in each of the Green Burn and Dargall Lane were regressed against the equivalent flow on the White Laggan over the common period of record. The resulting equations and associated goodness-of-fit values are reported in Table 5.2 and graphed in Figures 5.1 and 5.2. On the basis of these models the mean daily flows for the Green Burn and Dargall Lane for 198T and 1983 were simulated using the gauged flows on the White Laggan for those years. For elements where the rating relationship was not statistically significant (i.e. those not reported in Table 5.1) the annual output values (kg ha-1 yr-1) were produced as the product of the flow weighted mean annual solute concentrations (mg I-1) and the total annual discharge (m3 s_1) divided by the sub­ catchment area (m2).

Monthly inputs to both the Dargall Lane and Green Burn were determined in a similar manner to the annual inputs. Thus monthly inputs (kg ha-1) were derived as the product of the volume weighted monthly concentration (mg l"1) of each element in the bulk collector and the total monthly precipitation (cm). As with the annual data the total monthly precipitation was derived separately for both sub­ catchments and a linear increase in precipitation of 6% per 100m increase in altitude was assumed. In contrast to the annual loadings, however, it did not prove possible to make an allowance for the dry deposition of the major cations. This was due to an apparent storage of chloride within each sub-catchment in various months, a feature which will be discussed in more detail in section 5.4.

1.6- Q = 0.361Q0.79 DL WL ( c u m e c s ) 1.2- 1985

Figure 5.1 Simulated and Observed Flows - Dargall Lane 1985

(sosumo) jaw V 0) T3 4-1 0) ffl > •—1 3 0) £ W -P X3 to O Figure

5.

2

Monthly outputs (kg ha-1) from both sub-catchments were derived as the product of the flow-weighted monthly solute concentration (mg H) and the total monthly flow (m3 s_1), divided by the area of the sub-catchment (m2). This relatively straight-forward method was chosen in order to facilitate comparisons with predicted output budgets to be produced by the ILWAS model.