date	c(mg.L-1)
1940	0
1940.5	0
1941	0.025
1941.5	0.0375
1942	0.05
1942.5	0.0625
1943	0.075
1943.5	0.0875
1944	0.1
1944.5	0.125
1945	0.15
1945.5	0.175
1946	0.2
1946.5	0.225
1947	0.25
1947.5	0.275
1948	0.3
1948.5	0.325
1949	0.35
1949.5	0.375
1950	0.4
1950.5	0.435
1951	0.47
1951.5	0.645
1952	0.82
1952.5	0.76
1953	0.7
1953.5	0.7
1954	0.7
1954.5	0.755
1955	0.81
1955.5	0.575
1956	0.34
1956.5	0.4
1957	0.46
1957.5	1.105
1958	1.75
1958.5	1.925
1959	2.1
1959.5	2.1
1960	2.1
1960.5	1.98
1961	1.86
1961.5	1.21
1962	0.56
1962.5	0.975
1963	1.39
1963.5	1.035
1964	0.68
1964.5	0.68
1965	0.68
1965.5	0.91
1966	1.14
1966.5	3.61
1967	6.08
1967.5	9.73
1968	13.38
1968.5	11.73
1969	10.08
1969.5	10.01
1970	9.94
1970.5	9.775
1971	9.61
1971.5	10.96
1972	12.31
1972.5	16.695
1973	21.08
1973.5	24.045
1974	27.01
1974.5	27.07
1975	27.13
1975.5	29.01
1976	30.89
1976.5	34.185
1977	37.48
1977.5	40.005
1978	42.53
1978.5	42.06
1979	41.59
1979.5	41.59
1980	41.59
1980.5	41.645
1981	41.7
1981.5	41.7
1982	41.7
1982.5	43.935
1983	46.17
1983.5	45.7
1984	45.23
1984.5	46.58
1985	47.93
1985.5	51.4
1986	54.87
1986.5	55.635
1987	56.4
1987.5	64.045
1988	71.69
1988.5	73.22
1989	74.75
1989.5	76.1
1990	77.45
1990.5	77.215
1991	76.98
1991.5	72.155
1992	67.33
1992.5	67.385
1993	67.44
1993.5	67.795
1994	68.15
1994.5	69.735
1995	71.32
1995.5	71.205
1996	71.09
1996.5	70.56
1997	70.03
1997.5	64.32
1998	58.61
1998.5	58.845
1999	59.08
1999.5	59.61
2000	60.14
2000.5	59.49
2001	58.84
2001.5	60.43
2002	62.02
2002.5	61.31
2003	60.6
2003.5	58.72
2004	56.84
2004.5	55.955
2005	55.07
2005.5	54.89
2006	54.71
2006.5	54.24625
2007	53.7825
2007.5	53.5
2008	53
2008.5	52.855
2009	52.5
2009.5	52.25
2010	52
2010.5	51.9275
2011	51.7
2011.5	51.6
2012	51.46375
2012.5	51.3478125
2013	51.231875
2013.5	51.19
2014	51.15
2014.5	51
2015	50.9
