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Median annual inputs of nutrients and sediment in 2004–2012 to CB and the NAS are summarized in Table 2.1. NO_x (nitrate + nitrite) accounts for most of the TN load, whereas dissolved inorganic P (DIP) is a minor fraction of the TP load. Among the nine major tributaries, the Susquehanna contributes about 65% of TN and 46% of TP (Zhang et al., 2015). Relative to riverine inputs, inputs from direct precipitation to CB are small (7% of TN and 17% of TP).

Table 2.1 Median annual inputs of freshwater (Q, km³) and nutrients (10⁶ kg year⁻¹) to Chesapeake Bay (CB) and the northern Adriatic Sea (NAS) due to river runoff and precipitation (PPT) for the years 2004–2012

Parameter	CB	NAS
Rivers	PPT	Total	Western rivers	Northern rivers	Eastern rivers	PPT	Total
Q	54.7	13.8	68.5	52.6	5.9	3.2	9.4	71.1
TN	84.9	5.7	90.6	145.0	16.0	6.3	13.6	180.9
NOx	56.7	2.5	59.2	101.0	12.0	4.3	5.0	122.3
TP	5.2	0.9	6.1	8.1	0.4	0.1	1.1	9.7
DIP	0.7	0.2	0.9	2.7	0.1	0.04	0.9	3.7

Note: TN, total nitrogen; NO_x = nitrate + nitrite; TP, total phosphorus; DIP, dissolved inorganic phosphorus.

Compared with CB, riverine inputs of nutrients to the NAS are much higher (Table 2.1), with riverine inputs of anthropogenic nutrients to the western NAS (dominated by the Po River) accounting for 80%, 83%, 84%, and 73% of annual inputs of TN, NO_x, TP, and DIP, respectively. This reflects the higher population density in river watersheds of the western shore. Notably, nutrient inputs to the NAS are much lower than those to CB when normalized to the volume of the receiving water bodies (~1812 × 10³ kg N km⁻³ year⁻¹ for CB vs. ~285 × 10³ kg N km⁻³ year⁻¹ for the NAS). In addition, the TN/TP molar ratio for CB is much lower than for the NAS (33:1 vs. 41:1) while the NO_x/DIP molar ratio for CB is much higher than for the NAS (141:1 vs. 72:1).