This page contains a Flash digital edition of a book.
NO3-N mg L-1


GEO-6 Regional Assessment for North America ertilier itroen 9


Figure 2.4.17: Fertilizer use and nitrate concentration in groundwater at recharge, 1940–2004


20 15 10 5 0


1930 1940 1950 1960 1970 Year


20 40 60 80


0 1980 1990 2000 2010


Fertilizer use in the US has increased greatly since the 1940s, and nitrate concentrations in groundwater at recharge in agricultural areas have generally followed this trend. Source: DeSimone et al. 2014


of aquifers monitored had significant increases in nitrates, dissolved solids, and/or chloride concentrations. Trends in increased nitrate contamination of the nation’s shallow aquifers (Figure 2.4.16) reflect a similar increase in the use of nitrogen fertilizer from 1950 to 1980 (Lindsey and Rupert 2012; USGS report 2012-5049; Figure 2.4.17). Although nitrogen fertilizer use has levelled off since about 1990 in the US, recent continued increases in groundwater nitrate contamination probably reflect a lag effect between fertilizer use and detection of groundwater contamination.


Microbial pollution


Although not a widespread problem in North America, the main sources of microbial pollution include livestock, contamination from septic systems and combined sewer overflows during storms. Pathogenic organisms are difficult to monitor but are generally correlated with E. coli. The most commonly reported illness associated with oral exposure to contaminated water is gastroenteritis, which can cause severe dehydration due to vomiting and/or diarrhoea.


88


Pathogens in water are not monitored nationally in Canada; however, case studies in various agricultural regions suggest that pathogen contamination may be not uncommon – 80 per cent of surface water samples and 40 per cent of rural wells found evidence of microbial contamination (CCA 2013b).


The number of illness outbreaks associated with recreational waters in the US has been increasing, although the increases may represent an increase in reporting. The number of outbreaks per state is generally less than five per year.


Lake acidification


Although there have been improvements in the prevalence of acid precipitation since the 1980s, it continues to be a serious issue in some areas as a result of local soil and bedrock that are not able to adequately buffer the impacts. of acidic deposition, particularly in eastern North America. Problems in water chemistry remain even after large decreases in sulfate deposition (Clair et al. 2011). While studies conducted in eastern North America (and Northern Europe) have demonstrated that once lakes increase in pH >6.0, significant recovery of zooplankton communities can occur


(Gray and Arnott 2009). There is also evidence for declining calcium concentrations in temperate lakes that is a legacy of acid deposition (Jeziorski et al. 2015). Declining


Dermal exposure to sewage-contaminated water may result in infection of open cuts or rashes (Haile et al. 1999). The quality of waters used for recreation is generally assessed by measuring concentrations of indicator microbes, E. coli or faecal coliforms, typically found in high concentrations in human faeces. An elevated concentration of these microbes indicates that the water has been contaminated by human waste and is unsafe for recreational use – this happens most frequently after rain. In both Canada and the US, there are national guidelines for E. coli and faecal coliforms to ensure that recreational waters are safe, which health departments test for and close beaches when levels are unsafe. In the US, county and state health departments advise the public never to swim or surf within 72 hours after a rain.


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137  |  Page 138  |  Page 139  |  Page 140  |  Page 141  |  Page 142  |  Page 143  |  Page 144  |  Page 145  |  Page 146  |  Page 147  |  Page 148  |  Page 149  |  Page 150  |  Page 151  |  Page 152  |  Page 153  |  Page 154  |  Page 155  |  Page 156  |  Page 157  |  Page 158  |  Page 159  |  Page 160  |  Page 161  |  Page 162  |  Page 163  |  Page 164  |  Page 165  |  Page 166  |  Page 167  |  Page 168  |  Page 169  |  Page 170  |  Page 171  |  Page 172  |  Page 173  |  Page 174  |  Page 175  |  Page 176  |  Page 177  |  Page 178  |  Page 179  |  Page 180  |  Page 181  |  Page 182  |  Page 183  |  Page 184  |  Page 185  |  Page 186  |  Page 187  |  Page 188  |  Page 189  |  Page 190  |  Page 191  |  Page 192  |  Page 193  |  Page 194  |  Page 195  |  Page 196  |  Page 197  |  Page 198  |  Page 199  |  Page 200  |  Page 201  |  Page 202  |  Page 203  |  Page 204  |  Page 205  |  Page 206  |  Page 207  |  Page 208  |  Page 209  |  Page 210  |  Page 211  |  Page 212  |  Page 213  |  Page 214  |  Page 215  |  Page 216  |  Page 217  |  Page 218  |  Page 219  |  Page 220  |  Page 221  |  Page 222  |  Page 223  |  Page 224  |  Page 225  |  Page 226  |  Page 227  |  Page 228  |  Page 229  |  Page 230  |  Page 231  |  Page 232  |  Page 233  |  Page 234  |  Page 235  |  Page 236  |  Page 237  |  Page 238  |  Page 239  |  Page 240  |  Page 241  |  Page 242  |  Page 243  |  Page 244  |  Page 245  |  Page 246  |  Page 247  |  Page 248  |  Page 249  |  Page 250  |  Page 251  |  Page 252  |  Page 253  |  Page 254  |  Page 255  |  Page 256  |  Page 257  |  Page 258  |  Page 259  |  Page 260  |  Page 261  |  Page 262  |  Page 263  |  Page 264  |  Page 265  |  Page 266  |  Page 267  |  Page 268  |  Page 269  |  Page 270  |  Page 271  |  Page 272  |  Page 273  |  Page 274  |  Page 275  |  Page 276  |  Page 277  |  Page 278  |  Page 279  |  Page 280  |  Page 281  |  Page 282  |  Page 283  |  Page 284  |  Page 285  |  Page 286  |  Page 287  |  Page 288  |  Page 289  |  Page 290  |  Page 291  |  Page 292  |  Page 293  |  Page 294  |  Page 295  |  Page 296  |  Page 297  |  Page 298  |  Page 299  |  Page 300  |  Page 301  |  Page 302  |  Page 303  |  Page 304  |  Page 305  |  Page 306  |  Page 307  |  Page 308  |  Page 309  |  Page 310  |  Page 311  |  Page 312  |  Page 313  |  Page 314  |  Page 315  |  Page 316  |  Page 317  |  Page 318  |  Page 319  |  Page 320  |  Page 321  |  Page 322  |  Page 323  |  Page 324  |  Page 325